The invention discloses a grid power stealing user monitoring and positioning method comprising the steps of comparing the sum of current values at all load nodes of an outgoing feeder of a grid with the total value of current flowing into the load side of the grid to preliminarily judge whether there is abnormal power use, comparing the current error proportion of each branch with a preset current error proportion threshold, and finally, determining the position of a power stealing user. A system based on the method is further disclosed. According to the invention, there is no need for a lot of hardware and software investment, and the method and the system can be easily implemented with the aid of a computer.