The quick action section of differential protection is constructed by the electric charge on both sides of the transmission line as a physical quantity，which is a supplement to the existing configuration scheme of current phasor differential protection.This paper presents the basic principles，setting principle and realization method of change-of-charge differential protection，develops the experimental prototype，and carries out the dynamic simulation experiment for verification.The research has proved that，in the area of change-of-charge differential protection，the typical action time of fault is9～13ms，and the maximum time delay is15～16ms.In the case of fault outside the protection area，when the time of current transformer saturation is no less than5ms，the device is dependable but does not work，the protection principle having high safety performance.