The invention relates to an initial self-correction computation method of interface power in electrical power system hybrid real-time simulation, and belongs to the technical field of alternating current and direct current power grid digital simulation. Each electromagnetic transient simulation step size is achieved in the hybrid simulation, three-sequence power is calculated through three-sequence voltage and a three-sequence current at the positions of a subnetwork interface on the electromagnetic transient side and a subnetwork interface on the electromechanical transient side, a deviation is evaluated by using comparison of positive sequence reactive power and reference power, phase correction quantity of the three-sequence current of the subnetwork interfaces is output after an integration step, a threshold value is adopted to judge and determine the correction quantity in a steady state, therefore, the deviation of a phase quantity included angle of the three-sequence current and the three-sequence voltage at the positions of the subnetwork interfaces is corrected, and the initial self-correction computation of the interface power is achieved. The initial self-correction computation method is easy to implement, can reduce adjusting time, improves rapidity and stability of a system, and is a practical method for solving the problem that computation of the interface power in the current hybrid simulation is inaccurate. Meanwhile, the initial self-correction computation method is relatively small in calculated amount and suitable to the real-time simulation.