The utility model provides a topological structure of a double-clamping subunit. The topological structure of the double-clamping subunit comprises a first half-bridge submodule, a second half-bridgesubmodule, a diode D1, a diode D2, a first guide switch tube, a second guide switch tube, a bypass switch T1 and a bypass switch T2, the anode of the diode D1, the collector of the first guide switchtube and the collector of the second guide switch tube are connected with the anode of a capacitor C2 in the second half-bridge sub-module; the cathode of the diode D1 is connected with the anode of acapacitor C1 in the first half-bridge sub-module; the cathode of the diode D2, the emitting electrode of the first guide switch tube and the emitting electrode of the second guide switch tube are connected with the negative electrode of the capacitor C1 in the first half-bridge sub-module; the anode of the diode D2 is connected with the cathode of the capacitor C2 in the second half-bridge sub-module, the bypass switch T1 is connected with the second switch tube in the first half-bridge sub-module in parallel, and the bypass switch T2 is connected with the bypass switch T1 and the emitter ofthe third switch tube in the second half-bridge sub-module.