The invention discloses a chain type communication electric vehicle group sharing-decision frequency-modulation transaction method and system. An effective sharing decision frequency modulation and corresponding transaction method is provided for an electric vehicle group connected to a power grid or connected out of the power grid at any time. The number of nodes of the electric vehicle group canbe increased or decreased at will through chain type conduction communication, and it is guaranteed that the frequency modulation method is extremely excellent in expandability in a distributed electric vehicle access scene. Each electric vehicle can calculate the frequency modulation service power according to the service strategy selected by the electric vehicle, and performs the frequency modulation service of the power grid. Data integrity and safety are ensured through a forward transmission mechanism and a reverse transmission mechanism of the stored account book records. Meanwhile, theshared decision voting mechanism ensures the unforgeability of the transaction data, and a safe transaction mechanism is provided for the electric vehicle group to participate in the power grid frequency modulation service in the open environment. By orderly planning and controlling the charging and discharging of the electric vehicle, the purpose of assisting the frequency modulation of the power grid is achieved.