The invention discloses a pressure control method and a pressure control system for a transmission cavity. The pressure control method comprises the following steps of obtaining the current pressure value in the transmission cavity; making a comparison between the current pressure value in the transmission cavity and a target pressure value; and controlling the air inlet amount of an air inlet valve and the air extracting amount of an air extracting valve at the same time according to a corresponding relation between the pressure value in the transmission cavity, and the air inlet amount of the air inlet valve and the air extracting amount of the air extracting valve, to enable the current pressure value in the transmission cavity to reach the target pressure value. By virtue of the pressure control method and the pressure control system for the transmission cavity, it is ensured that the pressure in the technological process and the wafer transferring process of the transmission cavity can be almost kept constantly, so that backflow of participated gas and reaction side product to the transmission cavity caused by pressure fluctuation can be avoided, thereby better protecting the transmission cavity from being corroded and other damage; and in addition, by virtue of the control method and the control system, the current pressure value in the transmission cavity can reach the target pressure value within the shortest time, and minimum gas consumption is achieved.