Financial openness is an important part of financial supply-side structural reform,and it is an urgent question to be studied whether financial openness improve financing environ-ment and drive the innovative development of enterprises.Based on the data of A-share enter-prises from 2007 to 2020,this paper examines the influence and mechanism of financial open-ness on corporate innovation investment from the perspective of cross-border capital flow.This paper finds that financial openness significantly increases the R&D input of listed enterprises.The conclusion is still valid by using a series of endogeneity tests.Mechanism test shows that finan-cial openness increases the R&D input by easing overall financing constraints,reducing debt and equity financing costs,and increasing the scale of equity financing.Financial openness has a heterogeneous effect on different types of enterprises.The effect of increasing the R&D input by financial openness is more pronounced,if enterprises have non-state-owned property rights,small scale of assets,poor external financing environment and non-political-connection.Further research finds that with the improvement of intellectual property protection and informatization level,the promotion effect of financial openness on enterprise innovation investment has been strengthened.Finally,this paper also finds that financial openness has improved market per-formance and business performance of innovation investment.This study is helpful to understand the internal relationship among financial openness,financing environment improvement and corporate innovation investment,and the conclusions also have implications for the policy ad-justment of financial openness.