The invention discloses an energy storage unit active support control method and system based on a synchronous machine three-order model. A grid-connected inverter of an energy storage power station simulates a voltage source of a virtual synchronous machine, excitation control and speed regulation control are achieved, necessary inertia and damping characteristics are provided for a power grid system, and stable support of frequency and voltage of a new energy system is achieved. The control method gets rid of traditional phase-locked loop control, so the power angle control of the grid-connected inverter does not change depending on the change of a network frequency, necessary inertia and damping are provided for the new energy system, the autonomy and disturbance rejection of the control of the grid-connected inverter of the energy storage power station are improved, and the grid-connected frequency stability supporting capability and voltage stability supporting capability of the energy storage power station are improved.