Abstract: Establishment principle of equivalent trapezoidal thermal circuit model of a cable was explained, the method to divide insulation and soil into layers and to determine parameters such as loss, thermal resistance and thermal capacity was given, and the procedure to calculate cable transient temperature rise under arbitrary loads was presented. Then, the model and the program were verified by a case on a single-core cable, whose temperature rise under a step load current was simulated. Based on it, an equivalent scheme with a principle of equal thermal resistance was proposed for three-core cables, and by taking a 330 kV 3×1 000 mm² submarine cable as the example, temperature change curves under typical fluctuating loads of wind farms were calculated, with a good consistency with FEA simulation results. It was shown that thermal time constant of a directly buried cable was large, providing a good endurance for short-term or fluctuating overload current. The equivalent thermal circuit model and program algorithm could be used to assess the transient thermal response of single and multi-core cables, and to evaluate cable transmission capacity for fluctuating loads such as in wind farms, which was important for the optimization of cable selection and parameter design.