Although nowadays there are many electric power measuring methods in china,some of them still have many power theft preventing bugs.To measure big and middle consumers' electric power consumption ,it is hard to prevent consumers from stealing power energy by the means of current which is difficult to be checked up by relevant products and preventing stealing power energy technology, because of using CTs to converting current.The authors especially use the example of the three phase three element active electric power meter, analyses other power theft methods and summarizes the new preventing stealing power energy technology. In accordance with the characteristic of the power measuring and on the basis of the analyzing the right method of resolving the problem,the three phase four wire system power theft preventing device can detect all sorts of stealing ,especially to the stealing by the means of current in time and accutately.This device has acquired good effect in the application of power system.