The invention discloses a fiber reinforced plastic cement combined large-scale floating cover type methane tank. The fiber reinforced plastic cement combined large-scale floating cover type methane tank comprises a fermenting tank, a combined floating cover, a feed port, a discharge port and an exhaust port, wherein the lower part of the combined floating cover is a cylinder and the upper part of the combined floating cover is an arc-shaped sealed top cover; the cylinder consists of combined straight sheets; the sealed cover consists of combined inclined sheets; the sealed top cover is connected with the cylinder through a flange; and the outer surface of a floating cover fiber reinforced plastic skeleton is wound by steel wires and platinum pot glass fiber plastic woven meshed cloth and pasted by a mixture formed by mixing cement and various chemical industrial raw materials. The fiber reinforced plastic cement combined large-scale floating cover type methane tank is convenient to construct and has high strength, low cost, uniform pressure in the tank and long service life. The feed port of the fermenting tank is higher than the discharging port, so the waste can be discharged automatically. After the floating cover ascends and descends, a stirring device can guarantee that the materials and the liquid are mixed uniformly and the crusting phenomenon is avoided.