Abstract: The dynamic characteristics of a piston-connecting rod system was analyzed considering mixed lubrication of the piston pin bearing. The analysis method synthetically made use of the finite difference method(FDM)and the multi-body dynamic (MBD) method based on mode compression. Based on these methods, the mechanism of producing noise in semi-floating piston pin was studied. The effects of the piston pin bearing clearance, the maximum explosion pressure, and the engine speed on the piston pin noise were also analyzed. The results show that the piston pin noise is caused by the impact between piston pin and connecting rod small end bush, and the piston pin noise occurs at the time when the direction of the force on the piston pin bores reversed. A bigger piston pin bearing clearance or a higher engine speed can result in a greater piston pin noise. However, the maximum explosion pressure has little effect on the piston pin noise.