The present invention provides a phase failure diagnosis method based on current instruction reconstruction and negative sequence current extraction. The method comprises the following steps: calculating a d-axis current instruction value and a q-axis current instruction value of a motor according to the current torque, the rotating speed and the voltage of the motor; performing inverse Clark transformation and inverse Park transformation on the d-axis current instruction value and the q-axis current instruction value of the motor, to obtain a U-phase current reference value, a V-phase current reference value and a W-phase current reference value; calculating a reference negative sequence component of the U-phase current according to the U-phase current reference value, the V-phase current reference value and the W-phase current reference value; calculating a negative sequence component of the U-phase current according to the three-phase current; and calculating the difference between the reference negative sequence component of the U-phase current and the negative sequence component of the U-phase current, and performing phase failure diagnosis according to the difference between the reference negative sequence component and the negative sequence component. Therefore, phase failure diagnosis based on current instruction reconstruction and negative sequence current extraction is realized.