Abstract: The fracture failure reason of piston and crosshead of DW-34.7/(11.5-53)X type compressor was analyzed by means of chemical composition analysis, fracture analysis, mechanical properties testing and metallographic examination. The results showed that the main failure reason of compressor piston and crosshead was the unqualified microstructure.It made material mechanical properties can not satisfy the safe usage requests. At the same time, by reason of piston nut had not locking device, under alternating load, piston and piston rod had occured relative movement, resulting in the deterioration of the piston force, pistons first occurred failure accident，and high cycle fatigue cracks existed in crosshead, resulting in the next accident finally. At last, according to analytic results, the prevention measures were put forward.