For the purpose of improving the redundancy of the auxiliary power supply system of the metro vehicles, the grid connected power supply technology and the high-frequency converter technology were applied to line 4 and line 2 phase II project of the Ningbo metro. 4 SIV were grid connected to provide AC 380 V to the metro vehicles which grouping up with 4 motor cars and 2 trail cars. Meanwhile, 4 DC charger provided DC 110 V to the DC control circuit and the storage battery. The circuit composition, principle and characteristics of metro vehicle power supply system of Ningbo rail transit line 4 and line 2 phase II project were expounded. The application of grid connected power supply technology would improve the redundancy of auxiliary power supply system of metro vehicles.