Do the carbon trading policy and low-carbon city policy, as two typical carbon emissions reduction pilot policies, have a policy overlay effect on reducing pollution and carbon emissions? The multi-period difference-in-differences (DID) model was used to explore the policy effect of carbon emissions reduction policies on reducing pollution and carbon emissions from the perspectives of policy synergies and target synergies, basing on the panel data of 279 cities in China from 2006 to 2020. The results show that: (1) The dual pilot policy has an obvious synergistic effect on reducing pollution and carbon emissions. The longer the policy is implemented, the stronger the emissions reduction effect is. (2) The dual pilot policy reduces pollution and carbon emissions by optimizing energy consumption structure and promoting green technology innovation. (3) The implementation of dual pilot policy in western regions, non-resource-based cities, non-old industrial bases and developed cities has achieved better effect on reducing pollution and carbon emissions. (4) Both single pilot policies can promote to reduce pollution and carbon emissions. Comparison between two policies, the carbon trading policy play better effect on carbon emissions reduction, and the low carbon city pilot policy play better effect on pollution reduction .The double pilot policy is more effective than the single pilot policy in reducing pollution and carbon. The double pilot city that first becomes the low carbon city pilot and then implements the carbon trading policy has stronger effect on reducing pollution and carbon. This study provides a reference for implementing carbon emissions reduction policies.