Abstract: The electromagnetic field simulation software CST based on the finite integral method was used to simulate and analyze the influence of the metal plate on the distribution of the available test volume and external radiated field in the large-scale parallel wire-grid bounded-wave simulator. First of all, the simulation model of the parallel wire-grid bounded-wave simulator was established, and its rationality was proved according to GJB 8848. Then the influence of the metal plate on the electric field distribution of the available test volume inside the simulator was analyzed in detail, and the effect of the location, thickness, height, and length of the metal plate were listed through detailed data. Moreover, the shielding effect of the metal plate on the external radiated electric field of the simulator was discussed. Finally, several suggestions for setting the metal protection plate were proposed. The conclusion is a good reference for effectively shielding the external radiation field without affecting the internal electric field distribution of the bounded-wave simulator.