The CCT curve and TTT curve of as-cast 42CrMo steel were precisely simulated by using JmatPro software. The quenching process(which is as follow: quenching at 860°C by AQ251 quenching liquid and cooling to 200°C) was given by analysizing the CCT curve. The quenching microstructure, hot-stress field and hardness after quenching were simulated by using the Deform-HT module The results were obtained as follows:(1)The microstructure of the materials is martensite+bottom bainite at the surface and pearlite+ferrite at the centure.(2)The surface hardness and central hardness were separately 51.3 and 28.5 HRC. The metallographic observation and hardness experiment were done and the results of numerical simulation was finally verified.