The electromagnetic compatibility (EMC) testing standard requires that the electric drive system conduct EMC testing on a test bench under a simulated load. The shaft current generated by the test bench enters the interior of the anechoic chamber through a through-wall shaft, affecting the background noise of the anechoic chamber and the EMC testing results of the electric drive system. At the same time, the through-wall shaft passing through the shielding wall of the anechoic chamber can cause serious electromagnetic leakage. In this paper, the electromagnetic simulation model of the test bench and the semi-anechoic chamber is built, and the interference path of the shaft current and the shielding effectiveness of the system are studied. Through simulation, it is found that installing the shielding cover and grounding the test system can improve the shielding effectiveness of the test system. According to the standard, the actual load testing system is subjected to background noise testing, and the load testing system is optimized and designed based on electromagnetic simulation results. Ultimately, the background noise of the semi-anechoic chamber is lower than the GB/T 18,655-2018 5-level limit of 35 dBμV/m, verifying the effectiveness of the rectification and optimization.