NOVELTY - Dual-purpose biogas generating pit using high-temperature fermented straw and excrement in integrated two-step method comprises a fermenting tank and a biogas leading out pipe.    USE - The device is useful for agricultural applications.    ADVANTAGE - The shapes of the fermenting tank and the water pressure tank are the same, so the mechanical production is convenient. The device is placed integrally, which is convenient for transporting, it is mounted integrally, and it is simple and easy, it can be mounted by the farmers themselves; when the high-temperature fermenting gas output is super-high in summer, one straw fermenting tank can be closed for regulating the gas output. It completely changes the traditional manner of the marsh biogas generating pit, the straw is recycled and used in large amount through the domestic marsh biogas generating pit and solar energy in a simple and economical manner. It conforms to the renewable energy source plan of the country.    DETAILED DESCRIPTION - Dual-purpose biogas generating pit using high-temperature fermented straw and excrement in integrated two-step method comprises a fermenting tank and a biogas leading out pipe, where two straw fermenting tanks (1) and (2) and a gas generating tank (3) are connected in turn through a filter screen (14) in the tank, a marsh liquid circulating valve (16) and a corresponding pipeline, the two straw fermenting tanks are respectively mounted at the two sides of the gas generating tank (3), two straw fermenting tanks are mounted on the ground, the gas generating tank (3) is mounted on a cement mound (18) 300 mm higher than the ground, the conical top of a straw fermenting tank cover (6) is connected with a biogas leading-out pipe (11) by a biogas ball valve (7), the conical surface of the tank cover (6) is provided with an emptying ball valve (8) by a tee and is connected with a return ball valve (9), a return holding valve (10) and a bottom pipeline of a water pressure tank (13) by the tee branches, in the gas generating tank (3), a central axial line between the tank bottom and the tank cover (6) is vertically provided with a water pressure pipe (16), a lower nozzle of the water pressure pipe (16) is located at the tank bottom of the gas generating tank (3), the pipe wall 100mm away from the bottom of the gas generating tank is drilled with 2 water pressure pipe through holes (17), the upper part of the water pressure pipe (16) upwardly gets through the tank cover (6) in about 20mm and enters the water pressure tank (13) propped against the gas generating tank (3), the upper nozzle is vertically provided with a water pressure tank holding valve (12), the biogas leading-out pipe (11) gets through the tank cover (6) through the upmost part of the gas generating tank (3), is led out upwardly and is connected with biogas ball valves (7) of the two straw fermenting tanks, moreover, the water pressure tank (13) is reversely mounted on the gas generating tank cover and is opened with a vent hole (19) at the conical top of the barrel bottom, the tank mouth flange is hermetically connected with the gas generating tank (3) and the tank cover (6), the fermenting tank, the gas generating tank, the water pressure tank and the tank covers matched with the formers are fastened and sealed by a fastening bolt (4) and a sealing pad (5), and all the pipelines getting through the tank wall and the tank cover are spliced and sealed with the tank walls through which the pipelines pass.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the dual-purpose biogas generating pit.    Straw fermenting tanks (1,2)    Gas generating tank (3)    Fastening bolt (4)    Sealing pad (5)    Tank cover (6)    Biogas ball valves (7)    Emptying ball valve (8)    Return ball valve (9)    Return holding valve (10)    Biogas leading-out pipe (11)    Water pressure tank holding valve (12)    Water pressure tank (13)    Filter screen (14)    Marsh liquid circulating valve (16)    Water pressure pipe through holes (17)    Cement mound (18)