The invention discloses a fault diagnosis method for a multi-phase permanent magnet synchronous motor driving system. The fault diagnosis method comprises the steps of: (1) acquiring output signals ofa speed sensor, a DC bus voltage sensor and a phase current sensor of a multi-phase permanent magnet synchronous motor driving system to be diagnosed; (2) calculating a rotating speed index SI, a flux linkage difference absolute value |delta psi|, a harmonic plane current amplitude Ixy, a positive half-wave current index CI+ and a negative half-wave current index CI- separately by utilizing the signals acquired in the step (1); (3) performing fault diagnosis on the speed sensor; (4) performing fault diagnosis on the voltage sensor; (5) detecting a harmonic plane current state; (6) performingdefault phase fault diagnosis; (7) performing open-circuit fault diagnosis on an S1 switching tube; (8) performing open-circuit fault diagnosis on an S2 switching tube; (9) and performing fault diagnosis on the current sensor. The fault diagnosis method can realize rapid and precise diagnosis of various types of faults without additionally arranging an external auxiliary circuit.