The measurement of PD is a common non-destructive effect testing method to mornitor the defect existing in the insulation system. The power transformer is taken as an example in this paper to show how to restrain pulse interference led from high voltage side of transformer by using differential balanced method in the process of obtaining the PD signals, therefore making obtained signals more reliable. The principle of differential balanced method is discribed. The circuits of realizing shifting phase, amplitude modulation and differential amplification are presented. The antijamming effect of differential balanced method is compared and illustrated based on the testing data.