Abstract: Effects of tempering temperature on microstructure and mechanical properties of 0Cr6Ni5Mo martensitic stainless steel were studied by means of optical microscope,scanning electron microscopy,XRD and mechanical property test.The results show that the microstructure of the tempered steel temperated at temperature of 450—700 ℃ is composed of tempered martensite,retained austenite and δ-ferrite.With the increase of tempered temperature,the contents of retained austenite first increase and then decrease,which reaches a maximum of 29.8% at 600 ℃.While the strength of the steel first decreases sharply and then increases,reaches the lowest point at 600 ℃.All impact fracture morphology of specimens after tempered at different temperatures exhibits dimple pattern with features of plastic fracture,the tear ridge is clearly visible.