Abstract: In order to find the best heat treatment progress for X12CrNi13 martensitic stainless steel used for the couplings of control rod drive mechanism (CRDM) of pressurized water reactors (PWR), quenching and tempering at different temperatures were performed. Through microstructure observation, tensile testing, impact testing and hardness testing, the effects of heat treatment temperature on microstructure and mechanical properties the steel were studied. The results show that with the increase of quenching temperature, the austenite grain size continued to grow up, which lead to martensitic lath coarsening after quenching. With the increase of tempering temperature, martensite gradually decomposed, tempered microstructure gradually stabilized, carbides separated out and grow up, strength reduced, ductility and toughness increased. The tested steel had optimum microstructure and combination mechanical properties after quenching at 980 ℃ and tempering at 660 ℃.