The working principle of a single-cylinder engine intake system was deeply analyzed,and the gas fluctuation phenomenon in intake system was confirmed by working bench test.On this basis,the generating mechanism of gas fluctuation phenomenon in the single-cylinder engine intake system was deeply discussed.By virtue of the ideal gas equation,the speed-density equation and the mass conservation equation an intake gas dynamics model for the single-cylinder engine was founded.The Matlab/Simulink software was used to simulate the system.The comparative results between the numerical simulation and experiments show that the model for the single-cylinder engine intake system based on the speed-density method has a good accuracy.It can well reflect the intake value of the single-cylinder engine under volatile intake pressure.