Abstract: Composite divergent section is the key component of solid rocket motor nozzle, with the composite structure of ultra-thick and variable curvature to resist the comprehensive effects of high temperature, ablation, high-speed gas and mechanical load. Due to the low thermal conductivity of the divergent section, the characteristics of ultra-thick and the unreasonable curing cycle, severe overheating peaks are easy to appear during the molding process. In order to reduce the curing deformation and improve the forming quality of the divergent section, it is necessary to restrain the curing overheating and improve the curing uniformity. Firstly, the kinetics of high silica glass fiber/phenolic and carbon fiber/phenolic prepreg at 2 MPa were characterized by high pressure differential scanning calorimetry in this study. Then, considering the characteristics of multi field coupling in the molding process and the influence of molding die and curing process, the coupling model of curing process was constructed to analyze the phenomenon of overheating and non-uniform curing of the divergent section. Finally, the method of inserting a cooling process before vigorous curing was proposed to optimize the curing cycle and restrain the curing overheating. The results show that the optimized cycle can effectively suppress the overheating of the divergent section. After optimization, the maximum overheating peak decreases from 54.2℃ to 23.5℃, and the maximum curing degree difference decreases from 0.6 to 0.34, with the decrease ranges of 56.64% and 43.33% respectively.