In order to solve the basic scientific problems during the hot-press process of 300 ℃ resistant polyimide composites and promote application of polyimide composites in the main load bearing structures of weapons equipment， the chemical reaction properties of 300 ℃ resistant polyimide resin and the mechanical properties of the corresponding composites were analyzed by DSC、FTIR、rheology、TGA and mechanical properties test. The experiment results show that the polyimide resin is fully imidized at 230℃，the minimum viscosity of the polyimide resin is 86 Pa.s at the heating rate of 1℃/min， the corresponding polyimide composites produced by the optimized molding process exhibit good internal quality and mechanical properties.