To solve the problem that the electromagnetic interference (EMI) on balance signal when high power servo system is on work in wind tunnel, which will seriously affect the precision and reliability of the data, an EMI compensation method in time domain was studied. Introduce a by-pass circuit bridge to sense the interference signal, then compensate the balance signal by subtraction method. Simulate wind tunnel test environment, and carry out the inference compensation test for servo driver and high power motor. The results show that the method can reduce the EMI effectively, which can meet the demands of improving the precision and reliability of the data.