Abstract: In order to improve the efficiency of the Synchronous rectification Boost topology under light load conditions,quasi-square wave mode with soft switching（QSW-ZVS）is used instead of the triangular current mode（TCM）. With the help of gallium nitride（GaN）devices,the operating frequency of the converter can be further increased,and the power density can be improved. In order to ensure the realization of soft switching under high frequency conditions,this paper carries out precise mathematical modeling of the soft switching in QSW-ZVS mode. On this basis,it is pointed out that the realization range of soft switching can be extended by extending the time of synchronous rectification. This helps to improve the efficiency of QSW-ZVS mode under high frequency conditions. Finally,an experimental prototype with a rated power of 500 W is built. By realizing its soft switching in QSW-ZVS mode,the peak efficiency reaches 98.2%. The design goals of high frequency and high efficiency are achieved,which verifies the accuracy and correctness of the theoretical analysis.