Abstract: Since the reform and opening up, the development of private economy has been rapid. How to maintain the momentum of growth is the key problem that private enterprises need to solve urgently. It is the core competitiveness of private enterprises to have advanced innovation technology and efficient innovation efficiency. If innovation is integrated into the production activities of enterprises, it will promote economic growth; on the contrary, if it is integrated into non-production activities such as rent-seeking, it will restrict economic growth. Therefore, innovation is a necessary condition for the enterprise's development, and innovation performance is an effective criterion to measure an enterprise's innovation level. However, innovation performance is constrained by many institutional environmental factors, such as legal environment, preferential policies of the government, financial system and so on.Whether or not enterprises have political connections may affect their innovation performance. Private enterprises with political connections can enjoy preferential policies of the government and obtain financial subsidies. Under the condition of financing constraints, it is easier to obtain the funds needed for innovation through external financing. Scholars have verified the mechanism of the relationship between executive' political connections and innovation performance, but the results are different. Some scholars believe that executive' political connections have a positive impact on enterprise R&D and can positively promote the independent innovation of enterprises; some scholars have found that executive' political connections have a significant negative impact on technological innovation performance. Scholars have inconsistent conclusions about the relationship between executive' political connections and innovation performance. The main reason is that the relationship between executive' political connections and innovation performance is directly established in the process of analysis, which leads to a larger logical jump.Based on the SCP theory of industrial organization, the characteristics of executives such as executive' political connections do not simply directly affect innovation performance, but by means of mediating effects. This paper introduces the mediating effect of the governance behavior of the board of directors when analyzing the influence ofexecutive' political connections on innovation performance, explains the formation mechanism of innovation performance from the level of the governance behavior of the board of directors, and constructs the influence path model of " executive' political connections →the governance behavior of the board of directors →innovation performance ". At the same time, the relationship between the governance behavior of the board of directors and innovation performance are not a simple linear relationship. However, there may be a non-linear relationship. This paper uses the non-linear test method to verify the intermediary role of the governance behavior of the board of directors, so as to expand the existing private enterprise innovation research.This paper puts forward three research hypotheses:executive' political connections have a non-linear impact on the governance behavior of the board of directors, that is, logarithmic or inverted U-shaped; there is a non-linear relationship between the governance behavior of the board of directors and innovation performance, that is, logarithmic or inverted U-shaped; and between executive' political connections and innovation performance, the governance behavior of the board of directors plays a non-linear intermediary effect. In this paper, 5128 observation points of non-financial private listed companies from Shenzhen Stock Exchange from 2009 to 2013 are selected as initial samples. In order to improve the representativeness of samples, according to the usual practice, 3065 valid observations were obtained by eliminating ST or ST*, the existence of abnormal values, the serious lack of data, and the rapid change of the main industry (backdoor listing) soon after listing. Financial data, governance indicators, industry classification and other information come from Xenophon database. The information of R&D investment and political contacts of senior managers is obtained by hand. The author collects the annual reports of private listed companies from the website of Shenzhen Stock Exchange to find the data of R&D investment; downloads the executive resume from the CSMAR database; if the data is missing, then searches through Sina Finance, Trend Information, the company's official website and Baidu to determine whether there are political links according to the executive resume.The study finds that executive' political connections first affect the governance behavior of the board of directors, and then affect innovation performance. The mechanism model is expanded from simple "executive' political connections→innovation performance " to" executive' political connections →the governance behavior of the board of directors →innovation performance ". Thus, the formation mechanism of executive' political connections affecting innovation performance is explained more deeply and scientifically. At present, private enterprises are often constrained by lack of funds and do not have enough funds to innovate. In this situation, executive' political linkages can improve innovation performance by means of the governance behavior of the board of directors, which can play the role of "support hand" to facilitate corporate financing and reduce financing constraints. However, the cost of establishing political linkages is high. The role of the "hand of plunder" is prominent, the burden of enterprises is increased, the funds used for innovation or other investments are greatly reduced, and executive political linkages will have a negative impact on innovation performance through the governance behavior of the board of directors. Therefore, executive' political connections have a non-linear impact on the governance behavior of the board of directors, i.e. inverted U-shaped; there is a non-linear relationship between the governance behavior of the board of directors and innovation performance, i.e. logarithmic relationship; and between executive' political connections and innovation performance, the governance behavior of the board of directors plays a non-linear intermediary effect.The conclusion of this paper has some enlightenment for perfecting corporate governance theory and application practice: firstly, in private listed companies, executive's political connection affects innovation performance through the governance behavior of the board of directors. This is an imperfect performance of the internal governance structure of the company, resulting in low efficiency of governance. Therefore, in order to sustain the development of private listed companies, we should improve the governance system, supervise and control the executives in real time, strengthen internal governance, use funds appropriately and reasonably, optimize the allocation of resources, and actively participate in innovative activities. secondly, the government should formulate regulatory measures according to the actual situation of private listed companies. In the long term, the government functional departments should simplify administrative functions, optimize the investment environment of enterprises, better serve the development of enterprises, allow market participants to participate in market competition freely and fairly, and ensure the healthy development of private listed companies.

Key words:  top executives&rsquo, political connection, innovation performance, private listed companies, governance behavior, mediation effect