Abstract: Hydrophobicity recovery is the unique property of the silicone rubber composite insulator, and this property provides an important guarantee for maintaining the external insulation level of power transmission and transformation equipment, which is vital for the safety and stable running of the power grid. At present, it still lacks the efficient and quantitative method to evaluate the silicone rubber's hydrophobicity recovery property under running discharge conditions. In this paper, plasma was used to mimic the corona discharge occurred in high voltage running condition of the composite insulator to study the hydrophobicity loss and recovery process of silicone rubber. Based on the low molecular weighted siloxanes (LMW) diffusion theory and the Fick's second law, we established the physical model to shed light on the surface hydrophobicity recovery of silicone rubber. Moreover, the formula to calculate the LMW's diffusion coefficient D was educed by using the skills of mathematical approximation. The experiment results show that it takes only 3 minutes to modify the hydrophobic silicone rubber surface into completely hydrophilic. The value of LMW's diffusion coefficient D in the silica-like layer of silicone rubber is on the order of 10^-16 cm²/s. To compare the plasma treatment method with the pollution method, it is found that these two methods are equivalent, because the test results for the same series of samples using these two methods are in the same trend. Data obtained by the gas chromatography-mass spectrometry (GC-MS) indicate that, the total concentration of LMW in a silicone rubber decreases with the added aluminum hydroxide (ATH) in its bulk. Moreover, as the weight fraction of ATH increases in a silicone rubber, its hydrophobicity recovery rate decreases. The LMW's diffusion coefficient D obtained by plasma treatment method can be used as a parameter to quantitatively evaluate hydrophobicity recovery rate of a silicone rubber.