This study proposes a MHz isolated resonant converter, which achieves buck-boost DC/DC conversion, zero-voltage switching and the resonant components absorb the parasitic parameters. The DC analysis method and MATLAB computational algorithm are proposed for acquiring the specific circuit characteristics, including the voltage conversion ratio, the rms value of switch current and peak voltage of the semiconductors. The active power and apparent power are also analysed to provide design basis of optimising efficiency. The proposed converter shows greater advantages on voltage stress, current stress and efficiency over traditional isolated Sepic multi-resonant converter. A wide-output-voltage prototype based on the proposed converter was built in the lab and the experimental results verify the theoretical analysis well.