Abstract:     With China′s economic development entering a new normal state, the mode of economic growth is shifting from a traditional scale-up of extensive expansion to a quality-productive intensive model with technological progress as the core. The purpose is to push the supply-side reform by the demand-side inversion, upgrade production technology by using advanced standards. Force the upgrading of production technology, improve the competitive environment of the industry, and stimulate the innovation vitality of enterprises. By promoting the technology upgrading of related enterprises in the industry and upstream and downstream, we can better meet the growing consumer demand of customers. 
    The key to implementing the innovation-driven and transformation development strategy is to give full play to the decisive role of the market in resource allocation. In this process, it is especially important to use external partners to obtain market information and knowledge resources to promote technological innovation. In the market trading process, the customer as the downstream of the enterprise is the most direct stakeholder of the enterprise. How to stimulate consumption and expand demand through the buyer′s market, and then stimulate technological innovation, has become the key for enterprises to build core competitive advantage in the fierce competitive environment.
   In general, market power mainly affects innovation revenue through product pricing, market share, and entry threats. With the continuous development of industrial organization theory, the connotation and measurement methods of market power have been further expanded. Some scholars have pointed out that the bargaining power of the market participants through dominant position or special advantages is also an important source of pricing power and product market power, which will not only affect the enterprise′s ability to control the price of products, but also determine the profit distribution and innovation decision-making of enterprises.It is worth noting that with the rapid development of organizations such as open innovation and network innovation, more and more scholars regard the vertical market power formed by the bargaining between the buyer and the seller as an important factor affecting enterprise product market competition and strategic decision-making.
   From the perspective of market competition, the market power of an enterprise is a comprehensive concept, which includes both the market structure at the industry level and the influence of the industry competition environment, but also reflects the bargaining power generated by the buyer′s or seller′s concentration in the vertical transaction relationship.
   Based on the fact that enterprise innovation and R&D are influenced by industry competition and vertical transaction relationship, we put forward a question: what impact will downstream buyer market power have on enterprise technology innovation and R&D investment? Is it a positive "stimulating effect" or a negative "vertical squeezing effect"? Under different external market competition mechanisms, what are the characteristics of the impact and whether it will change?
    Customer is an important stakeholder in an enterprise, which has a wide and profound impact on enterprise behavior. Buyer market power is one of the important characteristics of enterprise customers. Buyer market power is one of the important factors affecting investment and financing decisions, performance and distribution policies of an enterprise. At the same time, the buyer′s market power plays an important role in the innovation decision-making process of enterprises. Therefore, this paper focuses on the impact of buyer market power on R&D investment.
   In terms of data selection, we take the A-share 610 high-tech companies listed in Shanghai and Shenzhen stock markets from 2012 to 2016 as the research sample, empirically tests the impact of buyer′s market power and market competition environment on enterprise innovation R&D investment, and further analyzes the effect of buyer power on enterprise innovation R&D investment under different market competition environment. 
   In the selection of variable indicators, we take customer concentration as the agent variable of buyer′s market power, and use the sum of the top five customers′ sales to measure the proportion of total sales in the same period. The higher the proportion, the more concentrated the customer relationship, the greater the downstream buyer′s market power, and the stronger the vertical dependence of the enterprise on it. In addition, we also measure the market competition environment from two perspectives of market competition intensity and market dynamics.
    In the aspect of empirical test, in order to test the relationship between buyer′s market power and market competition environment and enterprise′s innovation R&D investment, we construct a regression model, and test the change of buyer′s market power on R&D investment under different market competition environment by grouping market competition environment indicators.
    The results show that: the more intense the market competition is, the more obvious the "promotion incentive effect" of buyer′s market power on innovation R&D investment is; the stronger the market dynamics of enterprises′ industries, the more significant the "promotion incentive effect" of buyer′s market power on innovation R&D investment is.
    The theoretical contribution and significance of this study are as follows: Firstly, most of the previous literatures focused on the influence of horizontal market structure characteristics on enterprise technology innovation, but the literatures on the influence of buyer′s market power on enterprise innovation R&D investment based on the vertical perspective of industry chain is relatively rare. Therefore, the study on the relationship between the buyer′s market power and R&D investment is a supplement to the theoretical results. Secondly, this study combines the internal characteristics of the enterprises with the external market competition environment. On the basis of expanding the theoretical understanding of the relationship between market structure and technological innovation, it reveals more comprehensively and thoroughly the mechanism of the buyer′s market power in the field of technological innovation decision-making. Thirdly, this study breaks through the traditional game modeling method, and explores the interaction effect between buyer′s market power, market competition environment and enterprise R&D investment through empirical test. This study not only broadens the research horizon and methods, but also has important guiding significance for the decision-making of R&D and the improvement of innovation performance.

Key words: buyer′s market power, competition environment, competition intensity, market dynamics, R&D investment