Power cable conductor temperature is an important parameter to evaluate the ampacity and operation status of transmission line. However, the current cable temperature calculation model can not accurately describe thermal dynamic process of cable operation for ignoring the axial conductor temperature distribution. To solve this problem, a state space model of conductor temperature estimation considering axial heat conduction for middle and low voltage single core power cable was proposed in this paper which based on thermal equilibrium principle. To overcome the shortcoming that the thermal parameters are difficult to accurately calculate, a power cable conductor thermal parameter identification algorithm based on particle swarm optimization (PSO) was proposed. To verify model accuracy, a cable temperature experiment platform was established and the axial temperature of air laying power cable under various current was measured. Comparison of calculation results and experimental results shows that the precision of proposed model is higher than that of IEC 60287 model, the proposed model can meet the precision requirement of middle and low voltage power cable conductor temperature calculation under various current which can be applied to describe the single core power cable thermal dynamic process more accurately.