The metal shielding cavity can ensure the normal operation of the on-board recorder in the strong electromagnetic environment, but the heat dissipation and cable openings will reduce the electromagnetic shielding efficiency, so the structure needs to be optimized to improve the shielding efficiency. The influence of different opening schemes and structural parameters on shielding effectiveness is analyzed, and the calculation formula of electromagnetic shielding effectiveness is derived. Combined with the advantages of simple calculation by analytical method and accurate calculation by numerical method, the adaptive weighted PSO optimization algorithm is used to quickly find the optimization value of the analytical formula, and the numerical method is used to simulate the optimization result to calculate the fitness value, so as to obtain the final optimization result. The results show that compared with the pure numerical method, the calculation cost is reduced by 88.54%. Under the same shielding efficiency, the thickness of the shielding structure is reduced from 3.4 cm to 2.99 cm, and the volume is reduced by 9.03%; When the volume of the shielding structure is about the same, the shielding efficiency is increased from 98.79 dB to 102.65 dB. It can be seen that the proposed optimization method can greatly improve the design efficiency while improving the optimization effect.