NOVELTY - Biogas tank comprises a tank wall, and a spherical arch cover (3) which is equipped with an automatic stirrer (2). The upper part of spherical arch cover is set with a discharge tube (4) and a feedstock pipe (11). The spherical arch cover is set between a material feeding unit (5) and a feed chamber. The upper part of spherical arch cover is set with a cover plate. The cover plate is fixed with a discharging port, a fertilizer feeding port, a feeding port and a movable cover. The upper part of movable cover is fixed with a gas guide tube. The gas guide tube is connected to an appliance.    USE - Used as a biogas tank.    ADVANTAGE - The biogas tank comprising automatic stirring device is utilized for achieving automatic stirring-breaking of shells, and balanced gas production throughout the year (claimed); overcomes un-stabile air pressure; has high intensity, high illumination capacity, stable combustion property of appliance, and good sealing effect, so as to easily prevent air leakage problem under high pressure conditions by easy washing procedure, and exhibits uniform stirring procedure; removes slag easily; and can balance amount during all the four seasons.    DETAILED DESCRIPTION - Biogas tank comprises a tank wall, and a spherical arch cover (3) which is equipped with an automatic stirrer (2). The upper part of spherical arch cover is set with a discharge tube (4) and a feedstock pipe (11). The spherical arch cover is set between a material feeding unit (5) and a feed chamber. The upper part of spherical arch cover is set with a cover plate. The cover plate is fixed with a discharging port, a fertilizer feeding port, a feeding port and a movable cover. The upper part of movable cover is fixed with a gas guide tube. The gas guide tube is connected to an appliance by automatic stirrer.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of the biogas tank.    Automatic stirrer (2)    Spherical arch cover (3)    Discharge tube (4)    Material feeding unit (5)    Feedstock pipe (11)