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