The invention discloses a humidifying device. The humidifying device comprises an intake port, an exhaust port, a fan and a humidifying element, and further comprises a water inlet valve, a water accumulator for receiving humidified water from the humidifying element, and a pipeline, wherein the pipeline comprises a first pipe section and a second pipe section; one end of the first pipe section is connected with the water inlet valve, and the other end of the first pipe section is connected with the humidifying element; and one end of the second pipe section is connected with the water accumulator, and the other end of the second pipe section is connected with the first pipe section or the humidifying element. A first humidifying loop is formed in the position, from the water inlet valve to the humidifying element, of the first pipe section; and a second humidifying loop is formed from the water accumulator to the humidifying element via the second pipe section or by the second pipe section and the first pipe section. The humidifying device further comprises a water circulating device positioned in the second pipe section. The invention further discloses an operation method of the humidifying device. Through the humidifying device and the operation method thereof, the humidifying cycle is more flexible so as to adapt to various different operation conditions.