Abstract:      The improvement of the independent innovation capability of enterprises is an important indicator for the enhancement of national soft power. The innovation capability of Chinese companies has rapidly increased in the 40 years of reform and opening up. New and emerging companies represented by unicorn companies are constantly emerging. However, the occurrence of the "ZTE event" indicates that the independent innovation capability of Chinese enterprises is still weak in the international market competition. With the intensification of Sino-US trade wars, the improvement of Chinese enterprises′ independent innovation capability will be more and more restricted, which directly affecting the survival of enterprises and even the realization of strategic goal of the "Made in China 2025". In above, it can be seen that carrying out research on enterprise innovation has important theoretical and practical significance.
   Many factors affect the enterprise innovation. Past studies have explained it from the perspectives of institutional environment, market environment, financial constraints, corporate governance, executive characteristics and so on. In general, the key to improving the innovation capability of enterprises is to gather more resources and improve the level of optimizing and configuring limited resources. Especially, the "imprint" of the returnee executive′s foreign study or work experience will have an important impact on the agglomeration and optimization of enterprise resources.
    Although this issue has drawn attention since it was put forward, there is still no clear explanation on how returnee executive affect corporate innovation. On the one hand, it is well established that the utility of returnee executive increases the motivation of enlarging the company innovation. Dai O (2009) suggested that the high skill, expertise knowledge and international horizon from the returnee entrepreneur could be beneficial to increasing the firm innovation. Li et al. (2016) found that the Chinese company with returnee executive from the United States can more readily issue the American stock exchange securities to raise funds. 
   On the other hand, the inadaptability of returnees due to socially individual status can limit the enhancement of firm innovation. The medium-sized and small companies with CEO from abroad are not more fruitful in innovation behaviour than those without returnee CEO. Kenny M (2013) thought that the native entrepreneur is more important to achieve the increase of innovation behaviour than the returnees, and only during the business expansion does the returnee play a positive role after empirically analysing the samples from the information and communications technology (ICT) in China and India. In addition, the difficulty in building up trust within the administration of the native enterprise in China can also suppress the utility of returnee in raising the innovation behaviour.
    In addition, this paper also notes that the influence of returnees′ executives on corporate innovation is regulated by regional heterogeneity. Lin, Chen, and Lin (2018) ignored the impact of regional differences when analyzing the impact of returnees′ board members on corporate venture capital performance. However, based on the theory of new economic geography theory, it is difficult for returnees to overcome the problem of their inadaptability to the native inland enterprise with much weaker strength resulting from the limiting of the disadvantaged geospatial location. Simultaneously, due to the slower and fewer opening up of native market from the inland company, higher efforts from the inland firm and returnee can be taken to building up the trust with each other on the administration. Moreover, the slower response to the demand of market and the less benefit from policy result in the less utility of returnee in the inland company than the coastal one. 
    In contrast, it is well believed that the better location to business of coastal enterprise plays a greater role in utilizing and transferring the returnee labour to expand the market scale and produce the agglomeration effect in the past four decades of opening up. However, when the saturation of returnee in the coastal enterprise arrives, the agglomeration effect can produce the marginal diminishing so that the contribution to the firm innovation from the returnee would shrink. 
    Based on the analyses above, the proposed hypothesis was provided in the following: H1a: The returnee executive positively influences the innovation behaviour of company in China. H1b: The returnee executive negatively influences the innovation behaviour of company in China. H2: When the agglomeration effect from the returnee is below the threshold value, the marginal contribution to coastal firm of returnee would be larger than that to the inland firm. When the agglomeration effect from the returnee is above the threshold value, the marginal contribution to coastal firm of returnee would be smaller than that to the inland firm.
    To test the above theoretical assumptions，this paper utilize a typical sample of high-tech firms with available data in CSMAR. Our initial sample consists of 935 firm-year observations and our matched samples based on a multivariate propensity score consist of 885 firm-year observations. Firms are classified as treatment groups if a firm has at least one returnee executive, control groups otherwise. Second, the matched samples are used to assess the net effect of the role of returnee executives in the innovation behaviour by DID approach. We found that firm′s innovation is commonly increased through the introduction of returnees. Third, the results of regional heterogeneity analysis indicate that the average marginal contribution from the returnees of coastal enterprises is lower than that of inland enterprises which is contrary to the conclusion of previous literatures.
    This paper aims to make several contributions. Firstly, It is a deepening of the current research on the characteristics of executives that using specific types of executives as the entry point. Secondly, we investigate the specific association between the employment of returnee and the firm innovation with considering the geospatial heterogeneity from coastal area to inland. Finally, the modern approach of PSM-DID can efficiently solve the potential problems of mixed bias and selective bias with performing an examination.

Key words:  returnee executive, corporate innovation, regional difference, PSM-DID, policy effect