Abstract: Aiming at the cylinder pulling failure of marine diesel engine, the macroscopic and microscopic morphology characteristics, chemical composition, metallographic structure and mechanical properties of the fracture of piston skirt and cylinder liner were analyzed by direct reading spectrometer, optical microscope, scanning electron microscope and energy spectrometer. The results show that there were loose defects in the thin-walled hole of the piston skirt. These defects caused the fatigue cracking of the piston skirt, which reduced the matching gap between the piston skirt and the cylinder liner. The piston skirt and the cylinder liner were adhesively worn, and finally the cylinder pulling fault occurd.