Polyethylene cables would generate crack defects inevitably during long-term operation, which will cause partial discharge faults and threaten the normal operation of power grid. Polyethylene composite materials doped with microcapsules could realize the self-healing of cracks. In order to study the effect of microcapsules on the insulating properties of polyethylene materials before repair, we prepared pure polyethylene samples and polyethylene composite samples doped with different concentrations (0, 0.5%, 1%, 5%, 10%) of microcapsules, and their basic performance, volume resistivity, and AC electric strength were measured. The results show that the volume resistivity of composite samples doped with a small amount of microcapsules (≤1%) is significantly higher than that of pure polyethylene samples. But when the concentration is larger (>1%), the volume resistivity decreases. Compared with the pure polyethylene sample, the AC electric strength of the composite materials decreases, but when the concentration is no greater than 1%, the decrease amplitude is smaller, which could meet the normal operation requirements of cable. This is mainly related to the crystallinity of material, the interface effect between microcapsule and polyethylene, and the characteristics of microcapsule itself. In general, when the doping concentration of microcapsules is no greater than 1%, the insulating properties of the polyethylene composite material can meet the requirements of normal operation for cable.