Abstract: Strategic emerging industries as the focus of future development in China have been paid much attention by the central and local governments, a series of support policies have been introduced in succession , but the uncertainty of the promulgation and implementation of the relevant policies and the uncertainties arising from the process will affect the R&D investment activities of enterprises. This paper chooses strategic emerging industry-related enterprises as a research sample, based on the fact that the financing constraints affect the R&D investment of the enterprises, through the double angle of the suppression effect and the crowding out effect , we test the impact of policy uncertainty on R&D investment in emerging enterprises. The research results show that the policy uncertainty restrains the R&D investment of the emerging enterprises, and the uncertainty aggravates the financing constraints of the emerging enterprises and the tendency of fixed assets investment, and has the effect of suppressing and crowding out R&D investment. Further cross-sectional differential test found that policy uncertainty was more significant for private enterprises, aged enterprises, enterprises with lower marketization in the region.