In a contactless power transfer (CPT) system, a constant current determines the stability and power transfer capability of the entire system. We focused on track current constant control problems with load changes. We analyzed the influence of load changes on track current and acquired several factors influencing track current. We put forward a piecewise control strategy for phase shifting angle control in primary circuits of CPT systems. We conducted simulation experiments using MATLAB and Simulink. The simulation results indicate that the current stable time is less than 2 ms before and after switching, and show that the control method can control track current constant effectively.