TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Device: The biogas production and fermentation device also comprises a backflow unit located on one end of the anaerobic tank and connected with the spraying device, and four fermentation units which are installed two by two; where the backflow unit is located outside the four fermentation units. In the biogas production and fermentation device, the spraying device comprises an annular spraying pipe installed on inner edge at the top of the anaerobic tank and multiple spraying heads uniformly distributed on the spraying pipe; the backflow unit comprises at least one overflowing hole installed on one corner in the anaerobic tank, a backflow groove installed outside the anaerobic tank, a biogas backflow outlet pipe, a biogas backflow inlet pipe, a flower wall installed in the front of the overflowing hole, a manure leaking plate installed at the top of the flower wall, a filter net installed in the backflow groove, and a backflow pump installed at the bottom of the anaerobic tank; the anaerobic tank, overflowing hole, backflow groove, biogas backflow outlet pipe, and biogas backflow inlet pipe are connected with the spraying device in turn; the backflow pump is set with a pump lifting device; a big opening is installed at the bottom of the anaerobic tank; the bottom of the anaerobic tank is an inclined bottom; one end of the incline bottom props against the other end; multiple cross rods are bridged in the anaerobic tank in order to limit high-level position of the straw at intervals; the biogas outlet pipe is connected with the biogas collecting main pipe; a water sealing device is installed on the biogas outlet pipe; a constant-pressure device is installed at rear of the biogas collecting main pipe; the flexible cover is made of flexible material without skeleton; the flexible cover is fixed by the hanger convenient to assemble; a water sealing groove is installed at the top of the anaerobic tank corresponding to the edge of the flexible cover; and the water sealing tank is set with an emptying pipe and an overflowing pipe.