Humidifier, fuel cell system and humidity adjusting method

The invention discloses a humidifier, a fuel cell system and a humidity adjusting method, the humidifier comprises a shell, a pipe group and a valve, a separation part is arranged in the shell, an inner cavity of the shell is divided into a first cavity and a second cavity by the separation part, the first cavity is provided with a first inlet and a first outlet, and the second cavity is provided with a second inlet, a second outlet and a third outlet; a through hole is formed in the separation part; the pipe set is arranged in the second cavity and communicated between the second inlet and the second outlet, the pipe set is hydrophilic, the first gas and the second gas can conduct heat exchange at the pipe set, and the valve is arranged on the partition part. According to the humidifier disclosed by the invention, the regulation and control difficulty is reduced, the high-integration development of a fuel cell system is facilitated, the internal humidity of the fuel cell system can be effectively controlled,