The invention discloses a continuous casting tundish water port online baking bottom exhaust device and a method, belongs to the technical field of continuous casting tundish water port baking equipment and methods, and is used for online baking continuous casting tundish water ports. The device is characterized in that the upper end of a water port bottom exhaust pipe is connected with a water port lower port; the front end of a gas spraying pipe is fixedly connected to an L-shaped bending place of the water port bottom exhaust pipe; a nozzle direction of the gas spraying pipe is in an outlet direction of the water port bottom exhaust pipe; the back end of the gas spraying pipe is connected with the front end of a wind pressure hose; the back end of the wind pressure hose is connected with a compressed air distributor; and the compressed air distributor is connected with a compressed air pipe. The device adopts a gas spraying drainage technology to perform the water port bottom exhaust drainage by using compressed air, combines the water port bottom exhaust pipe with the gas spraying pipe to replace a high-power exhaust fan and an exhaust pipe, achieves the purposes of improving the bottom exhaust heat utilization efficiency and increasing the water port preheating temperature, and largely reduces the equipment investment and the energy medium cost.