The invention provides a method for controlling a slip mode variable structure of a brushless direct current motor based on a power exponential reaching law. The method comprises the following steps of S1, analyzing a mathematics model of the brushless direct current motor; S2, designing a slip mode controller; combining a power reaching law and an exponential reaching law, so as to obtain the improved reaching law-power exponential reaching law, and calculate the slip mode control rate at the current time; S3, setting a current loop and a speed loop for controlling the brushless direct current motor, wherein the current loop adopts the integral and proportional control type, and the speed loop adopts the slip mode variable structure control type using the power reaching law; S4, repeatedly updating the value of slip mode control rate i, so as to control the brushless direct current motor. The method has the advantages that the control quantity on the brushless direct current motor adopts three adjustable parameters, so that the control and adjusting are more flexible; a control strategy with high control quality, simple type and convenient implementing on the brushless direct current motor is provided.