The study uses data mining method to analyze the impact of mileage on the unqualified rate of vehicle emission inspection. The result of data mining shows that with the increase of mileage, the unqualified rate of commercial vehicles and noncommercial vehicles increased. Specifically, in the range of 0-200,000 km, the emission inspection unqualified rate of commercial vehicles is twice that of noncommercial. In the range of 200,000-600,000 km, the emission inspection unqualified rate of commercial vehicles is always higher than that of non-commercial vehicles. This result shows that mileage has a significant impact on vehicle emission status, and the unqualified rate of vehicle emission inspection is proportional to mileage mission inspection data.