It is difficult to implement traditional standby power supply automatic switching function in some substations, especially within weak power grid. Focusing on this circumstance, a wide area standby power supply automatic switching scheme based on smart grid is proposed. Based on three substations with weak interconnection, this scheme establishes one point for standby power supply automatic switching function. When a substation is losing its main power supply, a remote standby power supply will be switched on, in order to avoid the power grid fault caused by load loss. The scheme is implemented by the technology of smart grid information share and remote fiber optic communication network. This scheme can overcome some shortcoming of traditional standby power supply automatic switching unit, such as fixed action logic, limited application range, so as to expand standby power supply automatic switching function. The implementation of this scheme can strengthen the reliability of the power supply within weak power grid and realize the smart feature of smart grid.