In this paper, the properties of polydimethylsiloxane (PDMS), trialumina (ATH), and silicon dioxide (SiO2), as well as the properties of their composite rubber, were investigated. The findings indicate that silicone rubber exhibits a specific water absorption rate, ranging from 0.1% to 0.7%. Through gravimetric and thermogravimetric analysis, the “breathing” phenomenon of silicone rubber was observed, wherein the material absorbs water upon heating and releases it upon cooling. The dielectric response of silicone rubber with various formulations was examined using dielectric spectroscopy. The results demonstrate that the dielectric properties of silicone rubber are influenced by the presence of inorganic fillers (such as ATH and SiO2) and organic fillers (such as silicone oil) within the formulation. Notably, after water absorption, the dielectric spectrum of silicone rubber exhibited a significant shift, with the relaxation peak moving to lower frequencies and a marked increase in the dielectric loss tangent. The paper also underscores that hydrophobic pretreatment of hydrophilic fillers can mitigate water absorption and reduce the retention of water molecules within silicone rubber.