Abstract: Macroscopic observation, chemical composition analysis, hardness test, mechanical property test, metallographic examination and scanning electron microscope analysis were used to study the fracture reason of piston rod of a hydrogen booster compressor. The results show that the fracture reason of the piston rod was the improper heat treatment process of raw materials, which led to the decrease of the mechanical property of the piston rod, and the fatigue fracture occured under the action of high-cycle cyclic stress. Finally, the corresponding improvement suggestions were put forward for the reference of relevant personnel.