Abstract: In response to the thermal management challenges of a highly integrated electronic equipment module of a certain type of seeker under extreme working conditions, this paper proposes an optimized design method for the structural heat sink based on barium hydroxide octahydrate phase change material. Through the finite element analysis method, the influence laws of four gradient thermal conductivity enhancement configurations on the heat storage performance were studied, with a focus on revealing the coupling mechanism between the distribution density of the heat conduction ribs and the heat flow transmission characteristics. Based on the collaborative optimization of heat transfer enhancement and heat storage capacity, the composite structure of 16 grids combined with a central cylindrical rib was determined as the best solution. An experimental platform was built for verification, and the results showed that the effective temperature control time of the optimized phase change heat sink differed from the simulation results by only 3.2%, and the phase change equilibrium temperature deviated by only 2°C. This study provides a design concept that combines high energy storage density and efficient heat diffusion for the transient thermal management of on-board electronic equipment.