Accurately determining the relative position of the voltage sag disturbance source is significant for defining the responsibilities of both the power supplier and the consumer and the subsequent formulation of governance measures to improve power quality. Method for demarcating voltage sag disturbance source of distribution network based on phase comparison principle of positive sequence current fault component is proposed. Positive sequence fault component equivalent networks are established when different types of fault occur in different locations. Then the correlation between phase distribution of positive sequence current fault components and fault locations of all incoming and outgoing lines in substation are analyzed. Finally, the demarcation criterion and action boundary of the method for demarcating voltage sag disturbance source based on phase comparison principle of positive sequence current fault component are constructed. The method divides the disturbance source of the voltage sag, and only uses the current measurement information of the incoming and outgoing lines at the station. The measurement information is easy to obtain and has good engineering application prospect. The effect of voltage sag disturbance source demarcation is verified by modeling and simulating based on PSCAD when short circuit faults, phase jump and load disturbance occur.