Abstract: Heavy-duty railway traction power supply system has the characteristics of large traction load power, significant load fluctuation, regenerative braking energy and so on, which leads to the complexity and variability of the system power load distribution, and it is difficult for the traditional power load calculation method to effectively resolve the power load distribution of heavy-duty railway. Therefore, this paper establishes a mathematical model of the traction power supply system of heavy-duty railway and proposes a continuous power load algorithm adapted to the characteristics of heavy load. Taking a heavy-duty railway as an example, the mathematical model equivalence and power load calculation of its traction power supply system are carried out to verify the effectiveness of the algorithm in solving the system voltage, current and power distribution.