The work aims to obtain an efficient and time-saving union heat treatment process. 42CrMo was selected as specimen material and union as specimen model. Firstly, the improved heat treatment process was simulated by using software DEFORM and the simulation results were validated by experiments. The second improved heat treatment process was obtained by comparing the relationship between hardness and time, and was simulated by using DEFORM. The maximum hardness of the specimen surface obtained by simulation was 264HB and 297HB, respectively, the maximum hardness of the specimen surface tested was 278HB and 291HB. Under the same scheme, error of the maximum hardness obtained by simulation and experiment were 5.0% (Process I) and 2.1% (Process II), respectively, and fell in an acceptable range. Hardness of the specimen obtained by adopting improved process was about 9.54%~36.87% higher than that of specimen obtained by adopting conventional process. The maximum hardness of the specimen was 260HB and 285HB, respectively after the secondary improved heat treatment was simulated by using software. Compared with conventional process, its hardness requirement was fully met. By analyzing the results, heat treatment process improved for the first time fully meets requirement for hardness; that improved for the second time not only meets hardness requirement, but also greatly reduces processing time and improves production efficiency.