Forging process design is one of the difficulties in the manufacture of nuclear grade zirconium alloys, and it is also the key to obtain high quality products. For the processing of large-scale Zr-4 alloy ingots, Simufactforming software was used to simulate the forging process. Comparison of the simulation and actual temperature results for forging bar surface, combined with the microscopic observation of metallographic structure after forging, the influence laws of different processing temperatures on the microstructure of final forging billet were analyzed. The results show that compared with the microstructure obtained by the traditional forging process in β phase region, the grains size of forged billet under the optimized low temperature and high α phase zone is obviously smaller.The results of numerical simulation are agreed well with the results of actual forging test. The process design before forging and the forming mechanism of forging structure can be analyzed by finite element numerical simulation technology well. Thus, the numerical simulation technology can play a very good role in auxiliary analysis and has a high value to engineering application.