NOVELTY - The device comprises a fermentation tank fixed on a biogas collecting tank. The fermentation and biogas collecting tanks are respectively provided with a collecting cavity and a spherical cavity. An upper part of the fermentation tank is opened with a feeding port whose outer side is equipped with a feed opening. The feed opening is utilized for opening or closing a sealing door. An inner side of the fermentation tank is provided with other feeding port that is connected to a spaced sealing door. Upper and lower ends of the biogas collecting tank are respectively provided with a feed hopper.    USE - The marsh gas generating device is useful in fermentation process.    DETAILED DESCRIPTION - The device comprises a fermentation tank fixed on a biogas collecting tank. The fermentation tank and the biogas collecting tank are respectively provided with a collecting cavity and a spherical cavity. An upper part of the fermentation tank is opened with a feeding port whose outer side is equipped with a feed opening. The feed opening is utilized for opening or closing a sealing door. An inner side of the fermentation tank is provided with other feeding port that is connected with a spaced sealing door. Upper and lower ends of the biogas collecting tank are respectively provided with a feed hopper and a feeding port. The sealing door closes a lower end of the feeding hopper to block the feeding port. The fermentation tank is provided with a sealing and dividing cavity, a heating device, a temperature sensor, a pressure sensor, a fermentation chamber, a liquid collecting cavity, an air outlet and a liquid slag separating plate. The liquid slag separating plate is located in a horizontal plane. The air outlet is fixed with an automatic exhaust valve that is connected with the collecting cavity. A discharging pipe is passed through the biogas collecting tank that is connected with the fermentation chamber. The fermentation tank is connected with an upper end of the liquid slag separating plate. A lower end of the liquid slag separating plate is connected with the discharging pipe at an included angle of 150 degrees . The liquid outlet pipe is fixed on the fermentation tank. A lower part of the liquid collecting cavity is connected with a liquid outlet pipe. An upper part of the liquid collecting cavity is passed through the biogas collecting tank. The biogas collecting tank is fixed with a collecting marsh gas collecting pipe. The sealing door is provided with two sliding door plates. An outer side of the fermentation tank is provided with a sliding groove that is connected with the feeding port. A circuit board is fixed in the sliding groove. The sliding door plates are hinged on the fermentation tank. The fermentation tank is fixed with a cylinder whose two ends are provided with a piston rod and the swinging door plates. The heating device is provided with a water inlet pipe, a radiating pipe and a water outlet pipe. The radiating pipe is connected with the fermentation chamber. The water inlet pipe and the radiating pipe are connected with the water outlet pipe. The temperature sensor and pressure sensors are connected with a programmable logic controller (PLC) that is connected to the cylinder. The air outlet hole of the fermentation tank is fixed with an L-shaped air outlet pipe that is provided with a connecting part and an air outlet part. An automatic exhaust valve is fixed on the air outlet part.