The invention discloses a continuous annealing furnace decarburizing and nitriding device. The continuous annealing furnace decarburizing and nitriding device comprises a strip steel conveyor, a muffle furnace pipe, a humidifier, a hydrogen supply system, a nitrogen supply system and an ammonia supply system. The strip steel conveyor longitudinally penetrates through the muffle furnace pipe in thelength direction and is used for transporting strip steel. The muffle furnace pipe is sequentially divided into a decarburizing section, a nitriding section and a cooling section in the strip steel conveying direction. The decarburizing section of the muffle furnace pipe is provided with nitrogen-hydrogen mixed gas injection pipes, and the nitriding section of the muffle furnace pipe is providedwith ammonia-nitrogen mixed gas injection pipes. The hydrogen supply system and the nitrogen supply system are connected with the input end of the humidifier through pipelines. The output end of the humidifier is connected with the nitrogen-hydrogen mixed gas injection pipe through a first pipeline. The humidifier is connected with the ammonia-nitrogen mixed gas injection pipe after converging with the ammonia supply system through a second pipeline. The continuous annealing furnace decarburizing and nitriding device realizes the simultaneous decarburization and nitriding process of the cold-rolled strip steel, and improves the production efficiency, the decarburizing and nitriding process efficiency of the cold-rolled strip steel, and the surface state of the strip steel.