The inflow of foreign direct investment not only promotes China's economic development, but also brings environmental pollution. In order to analyze the nonlinear effect of FDI on CO2 emission, this study takes intellectual property protection as the threshold variable and uses the GMM method to construct a nonlinear dynamic threshold effect model for the impact of FDI on CO2 emissions in different regions on the basis of the inter-provincial panel data from 2005 to 2016. The research results show that FDI has a double threshold effect on CO2 emission in northeast China, and the optimal interval for intellectual property protection is (8.8939,10.4714), while there is no threshold effect in north China. The single threshold effect exists in the east coast, southeast coast, middle reaches of Yellow River, middle reaches of Yangtze river, northwest and southwest. In the middle reaches of the Yellow River, the optimal interval for the intellectual property protection level is higher than the threshold value, while the optimal interval for the intellectual property protection level is lower than the threshold value in the other five regions. All regions should reasonably determine the level of intellectual property protection and adjust the structure of investment , and reduce carbon emissions through financial incentives and technology sharing platforms.