The invention belongs to the technical field of motor fault detection, and discloses a method for establishing a direct-drive permanent magnet synchronous motor stator winding fault state mathematicalmodel. The method specifically comprises the following steps: 1, arranging four taps on each coil of the motor, and dividing each coil into three subunits; 2, writing an equation by taking the coil subunits as basic units, and establishing a DDPMSM mathematical model based on the coil subunits; and 3, building a calculation module of the model in Matlab/Simulink, so that the performance of the motor in different types of stator winding faults and health states can be conveniently and quickly analyzed. The beneficial effects of the method are that the provided mathematical model can analyze the stator winding fault and the performance of the motor in a healthy state on the premise that the topological structure of the model is not changed; and the influence of factors such as a winding type structure and a coil position is considered, so that the analysis precision of the model is greatly improved, and turn-to-turn short-circuit faults at different positions in the coil element can befinely analyzed.