In this paper, a half-bridge dual LLC converter with symmetrical autotransformer is proposed. The advantages of the proposed converter are that the dual LLC resonant tanks and symmetrical autotransformer can reduce the current stress of components, achieve high efficiency, and increase step-down conversion ratio and high power density. All active switches are turned on at ZVS and rectifier diodes are turned off at ZCS with wide load conditions. The operating principle and steady-state analysis are proposed. To verify the analysis, a laboratory prototype dual LLC resonant converter with input voltage of 400V and output 24V/21A is implemented. The maximum efficiency of the proposed converter is 93.4%.