Abstract: The change rules of microstructure and mechanical properties of A724GrC steel plate at different quenching and tempering temperatures were investigated by quenching and tempering tests. The results show that the optimum quenching temperature of the test steel is 890 ℃, and the optimum tempering temperature is 640-660 ℃. When the tempering temperature is higher than 680 ℃, the cementite decreases rapidly. As a result, the strength of A724GrC steel decreases sharply, which is below the required value. The quantity change of VC is much less than that of cementite, and it is not the main precipitated phase that affects the strength change.