How to raise the level of corporate innovation has become a key issue of common concern in theoretical and practical circles. Using a sample of China's A-share listed companies from 2007 to 2019, we examine whether common auditors contribute to corporate innovation. We find that companies employing the same auditors as companies with high innovation level have a higher level of innovation than companies employing different auditors. This indicates that the spillover effect on innovation behavior exists in companies employing the same auditor. Further, we find that common auditors promote corporate innovation by relieving agency problems and improving information quality. In addition, there is significant heterogeneity in the spillover effect due to different enterprise nature and different degrees of financing constraints. We not only add to prior literature about the examination of the factors affecting corporate innovation, but also help to understand the role of common auditors, which is of great significance to raise the level of corporate innovation and guide the healthy development of capital market.