Abstract: In the localization of martensitic stainless steel X39CrMo17-1 for valve internal parts, it was found that the mechanical properties were not up to standard. Comparative studies on X39CrMo17-1 steel were conducted in terms of different quenching and tempering processes by OM, SEM and room-temperature mechanical property tests. Results show that the microstructure and mechanical properties of X39CrMo17-1 steel can not be improved obviously when it is previously quenched at 1060℃ for different holding time or at higher quenching temperatures, and is then tempered at 750℃ for 3 hrs. A further microstructure analysis suggests that the steel is with the characteristics of hypereutectoid steel closed to eutectoid point. Consequently, it should be quenched and tempered at relatively low temperatures accordingly. The mechanical properties of martensitic stainless steel X39CrMo17-1 can be remarkably improved after being subjected to the optimized quenching and tempering process 1040℃/1 h+650℃/4.5 h, when an optimum coupling of plastic, strength and impact toughness can be reached, due to uniform distribution and dispersion of carbides in the form of tiny particles in X39CrMo17-1 steel.