Abstract: Insulation aging of power cables seriously threatens the safe and stable operation of power grid systems. Establishing the correlation characteristics between the insulation status of power cables and their temperature fields is of great significance. Leveraging COMSOL, a temperature field simulation model for the YJLW02-64/110 1×630 power cable under direct-buried laying conditions was constructed. The changes in the cable core temperature rise following the variation rules of the load current and ambient temperature under different insulation states were studied. Meanwhile, the variation law of the relative temperature rise of the cable core with the dielectric loss factor was analyzed, where the insulation state is characterized by the dielectric loss factor. The research results show that under normal insulation state (tanδ = 0.001), the cable core temperature rise exhibits an approximately quadratic increase with the capacities and a linear increase with the ambient temperature. When the insulation performance deteriorates (tanδ > 0.002), the relative temperature rise of the cable core is linearly proportional to the increase in the insulation dielectric loss factor. Then the dielectric loss becomes the dominant factor affecting the temperature change of the cable core, with the effect of capacity being significantly weakened and the influence of ambient temperature becoming almost negligible. Based on above findings, the least square method is employed to establish the functional relationship among the insulation material dielectric loss factor, cable core relative temperature rise, and capacity. A novel simplified evaluation method for power cable insulation state based on cable core relative temperature rise is then proposed. This method overcomes the limitation of traditional insulation condition detection for power cables, which requires synchronous acquisition of multiple parameters such as ambient temperature, capacity, and dielectric loss factor. It provides a new insight for constructing real-time insulation state perception systems and investigating the aging mechanism of power cable insulation.