Abstract: The effects of quenching temperature on microstructure, austenite grain size, tensile properties and delayed fracture properties of 30 MnSi steel bars were investigated, and the morphology of tensile fracture was observed. The results show that as the quenching temperature rises from 865℃ to 1 025℃, the tempered troostite and the few ferrite transforme into coarsened troostite, and the sizes of the austenite grains keep increasing, the coarsening and growing of the austenite grain obvious when the quenching temperature is 945℃; that with the increase of quenching temperature, the tensile strength and time for breaking of 30 MnSi steel bars increase and then decrease, and when the quenching temperature is 945℃, the 30 MnSi steel bar has the best delay fracture performance, no breaking within continuous 200 hours.