A new type of high-voltage and high-power double-clamp three-level converter is studied. Its working principle and double-clamp working mechanism are analyzed in detail, and its current path diagram is given.The voltage balance modulation of clamp capacitor and capacitor of upper and lower buses on DC side is analyzed. According to the characteristic that the current path can not change abruptly, a balanced control method is put forward, which can satisfy the discharge path of clamp capacitor by switching the switch state.Through the analysis of 64 kinds of space vectors, the vector combination satisfying the neutral point potential balance on the DC side is obtained, and the dual-balanced modulation strategy of the double clamp three-level converter is given.Finally, the validity of the modulation method is verified by the simulation of MATLAB and the experimental platform of the controller prototype based on DSP and FPGA.