A three-phase grid-connected inverter with high efficiency soft switching is proposed， which uses only one auxiliary switch and can realize zero voltage switching（ZVS） operation for all switching devices， as well as can suppress the anti-parallel diode reverse recovery voltage. Space vector modulation（SVM） strategy can be adopted for this inverter with the main and auxiliary switching devices operating at the fixed and same switching frequency. The soft switching process of this inverter is analyzed， and the design procedure for resonance parameters is described. A 20 kW prototype is built to verify the theory， and efficiency of the inverter with full load can attain to 98%.