Abstract: According to the measured pressure data of the four-stroke small utility gasoline engine, the cyclical variations of the maximum pressure, the crank shaft angle at the maximum pressure, the mean indicated pressure and the largest pressure rise rate were analyzed. Meanwhile, the influences of ignition advance angle, load and rotation speed on cyclical variation were also investigated. The test results show that the coefficient of cyclical variation, at the lower rotation speed and lower load, is larger than that at the full load and rated speed. Moreover, the combustion stability of the engine can be improved when the ignition advance angle is increased properly.