A mains supply method, wherein the method comprises: • upon a mains failure, detecting whether a quantity of remaining electricity of a backup mains supply system is less than a preset value, wherein the preset value is preset according to a quantity of electricity required for a critical load of a mains supply system to work properly for a time T, and the preset value is less than a maximum quantity of backup electricity of the backup mains supply system; • when the quantity of remaining electricity of the backup mains supply system is less than the preset value, controlling the backup mains supply system to supply electricity to the critical load, and detecting whether a quantity of feedable electricity of an electric vehicle of the mains supply system is greater than zero, wherein the quantity of feedable electricity of the electric vehicle of the mains supply system refers to a maximum quantity of electricity that can be provided for the critical load by all electric vehicles that use mains as a charging source and are being charged; and • if the quantity of feedable electricity of the electric vehicle of the mains supply system is greater than zero, controlling one or more electric vehicles that can provide a quantity of feedable electricity to supply electricity to the critical load, characterized in that the method further comprises: • when the mains works properly, if threshold power of the mains is greater than or equal to electricity supply power required by loads of the mains supply system, and the threshold power of the mains is less than a sum of the electricity supply power required by the loads of the mains supply system and charging power required by the electric vehicle of the mains supply system, detecting whether the quantity of remaining electricity of the backup mains supply system is greater than the preset value, wherein the loads of the mains supply system comprise the critical load and another device that needs the mains to provide electricity supply power, excluding the electric vehicle; and • if the quantity of remaining electricity of the backup mains supply system is greater than the preset value, controlling the backup mains supply system to supply electricity to the one or more electric vehicles, wherein a quantity of electricity provided by the backup mains supply system to the one or more electric vehicles does not exceed a difference between the quantity of remaining electricity of the backup mains supply system and the preset value. • upon a mains failure, detecting whether a quantity of remaining electricity of a backup mains supply system is less than a preset value, wherein the preset value is preset according to a quantity of electricity required for a critical load of a mains supply system to work properly for a time T, and the preset value is less than a maximum quantity of backup electricity of the backup mains supply system; • when the quantity of remaining electricity of the backup mains supply system is less than the preset value, controlling the backup mains supply system to supply electricity to the critical load, and detecting whether a quantity of feedable electricity of an electric vehicle of the mains supply system is greater than zero, wherein the quantity of feedable electricity of the electric vehicle of the mains supply system refers to a maximum quantity of electricity that can be provided for the critical load by all electric vehicles that use mains as a charging source and are being charged; and • if the quantity of feedable electricity of the electric vehicle of the mains supply system is greater than zero, controlling one or more electric vehicles that can provide a quantity of feedable electricity to supply electricity to the critical load, • when the mains works properly, if threshold power of the mains is greater than or equal to electricity supply power required by loads of the mains supply system, and the threshold power of the mains is less than a sum of the electricity supply power required by the loads of the mains supply system and charging power required by the electric vehicle of the mains supply system, detecting whether the quantity of remaining electricity of the backup mains supply system is greater than the preset value, wherein the loads of the mains supply system comprise the critical load and another device that needs the mains to provide electricity supply power, excluding the electric vehicle; and • if the quantity of remaining electricity of the backup mains supply system is greater than the preset value, controlling the backup mains supply system to supply electricity to the one or more electric vehicles, wherein a quantity of electricity provided by the backup mains supply system to the one or more electric vehicles does not exceed a difference between the quantity of remaining electricity of the backup mains supply system and the preset value.