The invention discloses a virtual synchronous machine control system under an unbalanced power grid condition. The virtual synchronous machine control system comprises a current collection module, a voltage collection module, a power calculation module, a voltage reference signal amplitude calculation module, a voltage reference signal phase information calculation unit, a three-phase voltage reference signal calculation module, a three-phase current reference signal calculation unit, an inverter three-phase modulation signal calculation unit and a pulse width modulation module. The invention further discloses a virtual synchronous machine control method under the unbalanced power grid condition. Required voltage/current positive and negative sequence separation and individual loop control in conventional control can be eliminated; the system control structure is greatly simplified; a virtual synchronous machine can transmit a balanced three-phase sine wave current to a power grid when the three-phase power grid is unbalanced; safe and stable operation of the virtual synchronous machine under the condition of an unbalanced grid voltage is ensured; and the control system and the control method have important significance in implementation of efficient and stable grid-connected operation of a new energy grid-connection device.