The evaporative emission and leak of vehicle fuel cause serious pollution to the environment. In order to find out the main influencing factors of the leak detection process of vehicle fuel evaporation system, the leak process and main influencing factors of vehicle fuel evaporation system were studied by means of simulation calculation and experimental research. The leak detection model of fuel evaporation system was established. The pressure decay process was simulated and calculated by matlab/simulink, and the calculated value was compared with the experimental value. The maximum relative error does not exceed 9.52%, indicating that the established mathematical model of pressure change is in good agreement with the test results, and the established mathematical model has high accuracy. Based on the positive pressure decay method, an experimental bench for leak detection of the fuel evaporation system was built, and the influence of different initial pressures and fuel volumes on the leak detection process of the fuel evaporation system under two leak hole diameters of 1 mm and 0.5 mm was studied. The results show that different initial pressures correspond to different decay rates. The greater the initial pressure is, the higher the pressure decay rate becomes. The higher the pressure decay rate is, the clearer the signal is, which is more conducive to leak detection. The fuel volume has a great influence on the pressure decay process, especially when the fuel volume is 80%, the difference in fuel volume is also 30%, and the pressure difference between 50% and 80% fuel volume is much larger than that between 20% and 50% fuel volume. Therefore, it is more important to select the appropriate range of fuel volume when conducting leak detection of the fuel evaporation system.