In this study, the biological electromagnetic dose variations and uncertainty caused by body weight differences in experimental animals were evaluated. An electromagnetic dose simulation environment of experimental rats under plane wave excitation was established using bio-electromagnetic simulation software and a three-dimensional digital model. The study frequency band was 0.1－6 GHz. The results showed that there was a linear relationship between the body weight of experimental rats and the whole-body average specific absorption rate under conditions of body weight disturbance. Below the resonant frequency point, the linear relationship was positive, whereas above the resonant frequency point, the linear relationship was negative. In the 1－6 GHz region, the degree of the linear fit was close to 1. The dose uncertainty for the experimental rats was investigated and a fitting calculation method was proposed. Combined with the experimental design case, the calculation process, calculation amount, and evaluation accuracy of the fitting calculation evaluation method were compared. The evaluation method had high accuracy and a low modeling calculation amount. The results of this study have certain guiding significance for the experimental design and dose evaluation of bioelectromagnetics.