With the increase of power system capacity and the shortening of circuit lines, more and more parallel reactors are retained for reactive power compensation. How to avoid the power system fault caused by DC offset due to high compensation is becoming a problem need to be studied. Firstly, based on the analysis of the mechanism of DC offset in compensating circuit, the influencing factors of DC offset are obtained. And electromagnetic transient simulation model is established based on ATP/EMTP. And the validity of simulation model is made by comparison of the simulation and 500 kV line test results. Cross impact characteristics of the different influence factors is got through the simulation research. And after the feasibility study of the phase selection closing, the advantage of the sequential time-delay phase closing method is put forward for the suppression of DC offset. This work is supported by Science and Technology Program Self-financing Fund of Hebei Province (No. 17212116) and Science and Technology Program of State Grid Corporation of China.