Rogowski coil is used to measure the current of the thyristor in ITER poloidal field converter, the output of the Rogowski coil is the differential of current over time, so the result should be synchronized with input signal by using the integrator. In the process of measuring, the integral drift is caused by the input offset current, input offset voltage and the input bias current, which produces errors which will be larger after a long time, so something should be taken to decrease the errors. Then a real-time way of compensation was proposed in this paper based on the foregoing analysis. According to the method, the high-performance integrator was designed and tested to fulfill the demand of decreasing the errors by simulation analysis and experimental test.