current longitudinal protection as a line, transformer, bus and other equipment differential protection, protection of vital movement is fast and accurate, compared with the traditional vector differential protection, differential protection speed has been greatly improved sampling value. This paper introduced process variable current algorithm, combining the advantages of sampling value differential protection, construct the current sudden variable sampling value differential protection criterion, and analyzes the value of R/S. Finally the application of MATLAB to the end of the line, phase short circuit as an example, the simulation of fault zone of the three kinds of differential protection, and the simulation results are analyzed.