In recent years, the buffer layer ablation failure in high-voltage (HV) cables has emerged as a critical fault that jeopardizes the safe and stable operation of power systems. To address this issue, this paper presents a single-component silicone rubber-based repair agent. The repair mechanism is elucidated through finite element simulations, while the impact of the repair agent on volume resistivity and water resistance was confirmed through experimental investigations. The simulation results demonstrate that the incorporation of the semi-conductive repair agent can effectively mitigate the occurrence of abnormal heating phenomena. Moreover, experimental findings reveal that the volume resistivity of the repaired buffer layer meets industry standards, registering below 1 × 105 Ω·cm when the mass fraction of carbon black exceeds 5%, while simultaneously retaining its water-blocking capabilities.