In order to solve the problem of high number of active devices and large circulating loss in existing auxiliary resonant inverters, a single auxiliary switch resonant inverter is proposed. The inverter can achieve switching twice by a single auxiliary switch in the switching period, which can replace the function of two auxiliary switches in most resonant inverters. At the same time, the auxiliary switch triggering time can be adjusted to reduce the duration of the circulating current loop and reduce the conduction loss, achieving the goal of reducing costs and increasing efficiency. Based on the equivalent circuit diagrams of the inverter under different working modes, the working principle of the inverter is analyzed. Finally, the proposed inverter is verified to achieve soft-switching of all switches by using the Matlab/Simulink simulation platform.