The invention provides a converter device of an electric railway ground auto-passing neutral section system. The device comprises a rectifier side single-phase multi-winding rectifier transformer T1,an inverter single-phase multi-winding inverter transformer T2 and a back-to-back four-quadrant converter; the device is used for conducting AC-DC-AC transformation on accessed alpha-phase and beta-phase traction busbar power supply, and supplying electricity to a catenary electricity sub-phase neutral section; a high-voltage winding is arranged on the T1 primary side, and n low-voltage windings and one high-voltage winding are arranged on the secondary side; n low-voltage windings are arranged on the T2 primary side, and one high-voltage winding is arranged on the secondary side; the secondary side high-voltage winding is connected with the secondary side high-voltage winding in series to be combined into voltage to supply electricity to the neutral section. Accordingly, the advanced power electronic converter device and a special transformer serve as core components, continuous power supply of the catenary electricity sub-phase neutral section can be achieved, a train can avoid powerfailure for the passing neutral section, no electric arc or overvoltage can be generated.