The invention discloses a marsh gas tank. The marsh gas tank comprises a soil pit, a marsh gas collecting tube, a raw material inlet pipe and a blow-off pipe, wherein four sides, the bottom and the top flat surface part of the soil pit are covered with a first impermeable membrane to form the bottom surface and the wall surfaces of the marsh gas tank; a second impermeable membrane is covered above the soil pit to form a covering surface of the marsh gas tank; the first impermeable membrane and the second impermeable membrane are overlapped at the top of the four sides of the soil pit, are adhered with each other, are fixed on the four sides of the top of the soil pit, and can be fixed by forming anchoring grooves on the four sides of the top of the soil pit and adding a pressing layer; the marsh gas collecting tube, the raw material inlet pipe and the blow-off pipe pass through a revetment and are extended into a hollow sealed space formed between the second impermeable membrane and the first impermeable membrane; the marsh gas collecting pipe is arranged close to the top part of the soil pit; the raw material inlet tube is lower than the marsh gas collecting tube; the blow-off pipe is lower than the raw material inlet pipe; and the raw material inlet pipe and the blow-off pipe are provided with sections extending toward the tank bottom. The marsh gas tank can also be provided with a pressure release pipe, wherein the part of the pressure release pipe outside the tank is provided with a gate valve. The marsh gas tank has the advantages of low construction cost, short construction period and no leakage.