The invention discloses a system and a method for controlling the furnace pressure of a continuous annealing furnace, and belongs to the technical field of rolling of a cold rolling plate strip. The system comprises a gas delivery module, a furnace pressure detection module, a furnace pressure judgment module and a furnace pressure regulation module, wherein the gas delivery module is used for injecting a protective gas into the continuous annealing furnace along the length direction of the bottom of a furnace shell through a pore plate; the furnace pressure detection module is used for detecting the actual furnace pressure of the continuous annealing furnace by virtue of a pressure transmitter; the furnace pressure judgment module is used for carrying out furnace pressure judgment on the actual furnace pressure and the furnace pressure of a set furnace area; the furnace pressure regulation module is used for regulating the furnace pressure of the continuous annealing furnace according to a furnace pressure judgment result by virtue of a control valve. The system and the method which are disclosed by the invention can be used for preventing the defect of oxidation tint caused because the furnace pressure is instantaneously reduced, ensuring the product quality, and reducing the nitrogen consumption; in addition, the system and the method which are disclosed by the invention can be used for setting the furnace pressure according to the yield of different continuous annealing furnaces, realizing the fact that the furnace pressure of the continuous annealing furnace is accurately controlled and effectively reducing the consumption of energy media.