Abstract: The present work proposes a calculating method for the relative diffusion coefficients of rejuvenation fluids designed for power cables. The predictive modeling methods are chosen for calculation. The Helmroth, Piringer, Brandsch, and Limm-Hollifield models are refined to determine these coefficients. The paper focuses on PMDMS, TMMS, and DMDB, which are the three primary components of rejuvenation fluids, and derives their relative diffusion coefficients in polyethylene. Additionally, molecular dynamics techniques are employed to simulate and obtain coefficients. The study performs a comparative analysis between the calculated values, simulated outcomes, and experimental data sourced from existing literature. The results show that among the four models, the Limm-Hollifield model is chosen for better accuracy and consistency in calculating the relative diffusion coefficients. Moreover, when compared to ordinary diffusion coefficients, computing relative diffusion coefficients is simpler and results in more comprehensible numerical values. Consequently, when selecting rejuvenation fluids, using the Limm-Hollifield model to determine relative diffusion coefficients is a more accurate and convenient approach to assess diffusion properties.