Using data of Chinese industry listed firms from 2006 to 2014，this paper examines the impact of stock pledge on enterprise innovation.Stock pledge is the signal of shareholders financial constraints.This study finds：（1）Stock pledge of controlling shareholder has a negative effect on enterprise innovation input；（2）The layer of pyramid structure will intensify the negative effective between stock pledge and innovation input；（3）Stock pledge of other large shareholders will intensify the negative effective between stock pledge and innovation input.From the perspective of agency theory，this paper not only reveals the stock pledge influence mechanism on enterprise innovation input，but also provides empirical evidence for enhancing investor protection.