For the problem of multiple processes and high die cost when forming a small casing by bar extrusion, it was proposed to use tube extrusion process to replace it, thereby reducing the process related to hole forming. Firstly, the forming simulation of the original process was conducted by using numerical simulation software Deform-3D to verify the reliability of the modeling results such as material model. Secondly, a simulation analysis of the new process was conducted, and it was found that there were folding defects in the casing head after forming, which was consistent with the actual test results. Then, the causes of defects were analyzed, and the solutions were proposed to improve the die structure. The results show that when the lower die is floating and the top ring position is set appropriately, folding defects can be avoided, and the tube extrusion forming can be completed to obtain the casing parts with better forming effects. After actual production verification, the new process can meet the production requirements, and the quality of the formed casing parts is good, without various defects such as folding. Compared with the original process, although the billet price is higher, the die cost is lower, the material utilization rate is higher, and overall cost reduction is achieved.