The invention provides an arm simplification method of a modular multilevel converter suitable for real-time simulation. The method consists of six steps. According to an MMC three-phase six-arm electrical positive sequence, negative sequence and zero sequence expression and an instantaneous power fluctuation and sub-module capacitance voltage fluctuation expression, and the MMC arm simplified method suitable for real-time simulation is proposed. The arm simplification method is advantaged in that simulation efficiency is greatly improved while simulation accuracy is guaranteed, and the arm simplification method is suitable for real-time simulation under MMC steady-state conditions.