how to promote the corporate investment is one of important and difficult issues faced by government. This paper studies the effect of accelerated deduction of input VAT on investment. The DID test based on No.70 fiscal and tax notification in 2018 shows that the test sample companies improve the investment significant after the policy promulgation compared to control sample, but the effect mainly exists in ordinary capital investments. The further research finds that the financial constraint is the main mechanism underlying the phenomena. Our paper shows that the financial constraint is main obstacle to investment and accelerated deduction of input VAT will bring about positive effect on investment.