The invention relates to a high-efficiency DC-DC converter which comprises a first full bridge, a second full bridge and a third full bridge, wherein the first full bridge, the second full bridge and the third full bridge are identical in structure. Bridge arms of the full bridges are all connected with an input power supply in parallel, and the difference between the phase position of the first full bridge, the phase position of the second full bridge and the phase position of the third full bridge is 120 degrees. An on-bridge tube of the advancing bridge arm is driven first, and an under-bridge tube of the advancing bridge arm is driven half a period later than the on-bridge tube. An on-bridge tube of the lagging bridge arm is driven X periods of time later than the on-bridge tube of the advancing bridge arm. Due to the fact that in the five states for energy transmission at each order, at least one phase and at most two phases of the first full bridge, the second full bridge and the third full bridge work, in the whole process, currents are shared by the full bridges which work simultaneously, the current load of each full bridge is reduced, as a result, circuit loss is lowered effectively, the current limiting problem generated during power amplification through a traditional full bridge is solved, and the current resisting requirement of a device is also lowered. Due to the fact that the soft switching state is realized in a part of period, switching tube loss caused by the hard switching state of a switching tube is lowered, and the conversion efficiency of the DC-DC converter is improved.