Multiwinding transformer + H-bridge converters is a typical topology in high-voltage and high-capacity power electronic applications. Based on the analysis about the high frequency characteristics of a PWM controlled H-bridge and the high frequency equivalent model of the topology, the theoretical foundation of how carrier phase-shift control suppresses high frequency harmonics is derived, and a broader rule of carrier phase-shift angle is provided. The results of simulations and experiments prove that with the appropriate carrier phase-shift angle, the high frequency harmonic can be suppressed to a low level, when there is no filter at the port of H-bridge. And this can simplify the topology, reduce the cost and decrease the failure rate.