Disclosed is a method of communicating between an electric vehicle, a supply equipment, and a power grid, which is performed by an electric vehicle communication controller of the electric vehicle, the method including an operation of transmitting a discharge schedule including the amount of energy discharge, a discharge start time, and a discharge finish time to a supply equipment communication controller of the supply equipment or a power grid communication controller of a power grid operation server, receiving a discharge cost calculated according to the discharge schedule from the supply equipment communication controller or the power grid communication controller, and transmitting an authorization message for the discharge cost to the supply equipment communication controller or the power grid communication controller.