The invention relates to a differential circuit protection method, and the method comprises the following steps: (1) setting N sampling branches in a differential circuit, wherein each sampling current branch is connected to a protection device through a plug connector, and the positive and negative polarities of the plug connectors of the M sampling branches are oppositely inverted to be connected into the protection device, and N >M>= 1; (2) during the calculation of the unbalanced current values of the N sampling branches, performing phase inversion processing on the currents of the M sampling branches, and adding the currents of the M sampling branches and the currents of the other N-M sampling branches to serve as actual unbalanced currents of the N sampling branches; (3) performing differential protection action according to the unbalanced current. On the basis of not changing the hardware loop of the original protection device, the unbalanced differential current caused by powerfrequency interference can be eliminated only by adjusting the wiring mode of part of terminals of the sampling branch, so that the reliability of differential protection is improved.