The invention provides a closed-loop control method and system for automatically controlling pressure to implement well killing. The method comprises the steps: setting a pressure value and a maintaining value of a control meter pressure according to a preset assignment value, starting a closed-loop control process, and monitoring the pressure value and the maintaining value of the control meter pressure in the closed-loop control process; when the difference value between the pressure value and the maintaining value is higher than a first preset allowable value, adjusting the opening of the valve in a preset mode to enable the difference value between the pressure value and the maintaining value to be smaller than the first preset allowable value; adjusting the opening of the valve according to a preset declining mode, and after preset time, comparing the difference value between the pressure value and the maintaining value with a second preset allowable value, and when the differencevalue between the pressure value and the maintaining value is higher than the second preset allowable value, adjusting the opening degree of the valve in a preset fine adjustment mode to enable the difference value between the pressure value and the maintaining value to be smaller than the second preset allowable value.