Abstract：In the LLC resonant circuit, in order to calculate the parameters of the resonant elements Lr, Lmand Cr, the half-bridge three-level LLC resonant circuit applied to the electric vehicle charging pile was taken as the research object, and the working mechanism of the circuit was analyzed. The control strategy of the each pair switch-off time interleaving ( one turned off, and then the other turned off) was adopted to achieve the work status of the circuit in the zero-voltage shutdown and the purposes of reducing switching losses and soft switching. Based on the simplified fundamental component modeling method, the circuit mathematical model was established, and the parameter design method of Lr, Lmand Crfor LLC resonant elements in half-bridge three-level circuit was obtained through theoretical derivation. A prototype of the input voltage ranging 600 ～ 750 V and the output of 750 V/20 A was designed, and the correctness of the above theoretical analysis and the rationality of the proposed design method were verified.