The invention discloses a high-gain passive lossless clamped inverter comprising a three-winding built-in transformer structure. The high-gain passive lossless clamped inverter comprises two input inductors, two power switch tubes, two clamping diodes, two output diodes, two clamping capacitors, an output capacitor and a built-in transformer with three windings. The built-in transformer is utilized to expand voltage gain of the inverter and lower voltage stress of the power switch tubes, leakage inductance of the built-in transformer is utilized for realizing zero current turning-on of the switch tubes and inhibiting reverse recovery current of the output diodes, the clamping diodes are turned off automatically, the problem of reverse recovery is avoided, a clamping circuit formed by the clamping diodes and the clamping capacitors effectively absorbs voltage spike when the power switch tubes are turned off and realizes lossless transfer of energy, the circuit structure is simple, control is facilitated, and the inverter is applicable to high-gain and high-efficiency grid-connected photovoltaic power generation transformation occasions.