In this study, the issues of unclear characteristics of dose differences in multi-frequency and large-sample bioelectromagnetic exposure systems were studied. For this, four contrast simulation environments were established using Sim4Life. The frequency points in the simulation were set to 1.8, 2.4, 3.6, and 5.8 GHz, respectively. The scattering field and whole-body average specific absorption rate (WBASAR) values were simulated and analyzed. The results revealed that the WBASAR value for experimental animals was influenced by the electromagnetic scattering of adjacent animals, and the spatial distribution of the WBASAR value was similar to the trend followed by the excitation field distribution. The excitation field was the primary factor causing the variation in the WBASAR distribution. In addition, the WBASAR distribution varies with frequency, and a higher ratio of body size to wavelength inhibits the WBASAR variation. Furthermore, a design suggestion for the exposed platform was proposed to reduce group dose uncertainty based on the variation characteristics. Overall, this study provides a dose evaluation basis for the design of electromagnetic exposure systems.