A portable emission measurement system (PEMS) was used to perform a real driving emission(RDE) test on three China 6 light-duty vehicles to study the impact of cold starting on real road driving on CO and NO_x emissions. The CO₂ moving average window method was used to process the test data of these vehicles, and compare the contribution rate of CO and NO_x emissions and the mileage of the road section in the urban area and the whole process at different coolant temperatures. It is found that the CO and NO_x emission factors including cold start are 10.45%~53.12% and 8.91%~38.74% higher than those of without cold start for gasoline vehicles, and 62.60%~96.67% and 2.11% ~ 4.79% higher for diesel cars; Lower engine temperature leads to serious CO emissions from both gasoline and diesel engines, and low coolant temperature has a certain inhibitory effect on diesel engine NO_x emissions. It is recommended that the follow-up emission regulations pay more attention to the cold start emissions of the RDE test.