Abstract：Based on the data of Shanghai-Shenzhen A-share listed companies from 2007 this paper empirically tests the impact of stock liquidity on R&D investment and the mediating role of financing constraints and two types of agency costs by using regression analysis and mediation effect testing procedures.The results of the study are as follows:(1) There is a significant positive correlation between stock liquidity and corporate R&D investment,indicating that stock liquidity will promote R&D investment;(2) Stock liquidity significantly reduces financing constraint and second-class agency costs,thereby improving the R&D investment, and financing constraints and the second type of agency cost of the enterprise play a partial intermediary role in the process of stock liquidity affecting R&D investment;(3) The first type of agency cost plays a regulatory role in the process of stock liquidity affecting R&D investment. The higher cost of the first type of agency, the more significant the effect of stock liquidity on the R&D investment of enterprises. In order to overcome the endogeneity of the model, this paper chooses margin financing business as a quasi-natural experiment. By constructing the propensity matching score and the double difference estimation model, the results still support the research conclusions of this paper.

Keyword：Stock Liquidity;R&D Investment;Financing Constraint;Agency Cost;