The invention discloses a method and system for controlling stability of voltage of an ultra-high-voltage direct-current layered feed-in power grid, and belongs to the technical field of electrical power systems. The method comprises the following steps: acquiring a low-value threshold UcthL, a high-value threshold UcthH and a set time threshold delta Teth of a voltage Uc of commutation buses of ahigh-end inverter and a low-end inverter; monitoring the voltage Uc of the commutation buses of the high-end inverter and the low-end inverter and the lasting time delta Te of the voltage Uc in realtime by using a voltage acquiring and measuring device; and when the voltage Uc of the commutation buses of the high-end inverter and the low-end inverter is smaller than the set low-value threshold UcthL and the lasting time delta Te is longer than the set time deltah Teth, starting direct-current power emergency fall-back control, and when the voltage Uc of the commutation buses of the high-endinverter and the low-end inverter recovers to be increased and is greater than the high-value threshold UcthH and the lasting time delta Tr is longer than the set time threshold delta Trth, starting direct-current power slow-speed increasing control. The stability of the voltage of the ultra-high-voltage direct-current layered feed-in power grid is controlled, and stable running of an alternating-current and direct-current parallel and series system is ensured.