The invention relates to a combined methane tank, which belongs to the field of a methane generating device. The combined methane tank is composed of an upper tank body, a lower tank body, a locking hoop, a gas tank cover, a feed pipe and a slag discharging pipe. The upper tank body and the lower tank body are connected through the locking hoop and a locking bolt, and the feed pipe and the slag discharging pipe are respectively installed at both sides of the lower tank body; a gas tank opening is arranged at the top part of the upper tank body, and a floating-proof fence is installed in the lower tank body, being convenient for steeping the fed fodder in the fecal sewage. Because the upper tank body and the lower tank body adopt the combined type, and the shape thereof adopts a cone with gradient, the transporting of the methane tank is convenient, the sealing effect is good, and the service life is long, so the industrial fabrication can be adopted. The combined methane tank solves the problems of the currently used methane tanks in rural areas that the structure stability is poor, both the corrosion resistance and the freezing resistance are poor, the service life is short, and the sealing effect is poor, so the anaerobic bacteria fermentation and the methane generation are directly affected. In addition, respective household methane tanks are connected into a whole, solving the problem that normal use is affected due to gas cut caused during the feed input or the methane tank cleaning, so the combined methane tank is especially suitable for being used in rural areas.