In order to realize the hot extrusion molding of high quality propellant, the hot extrusion molding process of propellant grain based on numerical simulation was analyzed. The basic model of a polymer fluorocarbon propellant was established, and the extrusion process of solid propellant was simulated by polyflow software. The pressure distribution, velocity distribution, and the change trend of expansion rate of the solid grain in the constant pressure and constant speed extrusion process were analyzed, and the relationship between different grain sizes and process parameters was explored. The results show that the best forming process of solid grain is constant speed extrusion process, the main process temperature range is 60 - 80 ℃, and the inlet volume flow rate range is 5. 10 × 10-9 - 1.02 × 10-8 m3/s.