Abstract: Fracture failure of a 2507 super duplex stainless steel piston rod occurred during operation. The failure of the piston rod was analyzed by chemical composition detection, mechanical properties test, OM and SEM observation and ANSYS finite element analysis. The results show that the chemical composition of the piston rod meets the standard requirements, but the mechanical properties do not fully meet the standard requirements. The failure mode of the piston rod is brittle fracture, and the failure location is in the heat affected zone near the base material. Improper heat treatment process leads to the precipitation of a large amount of harmful σ phase in the structure, and it fails under large alternating load. The precipitation of σ phase can be reduced or even avoided by appropriately increasing the solid solution temperature to 1050-1150 ℃ and increasing the cooling rate, so as to improve the microstructure and comprehensive properties of the piston rod.