An apparatus for biologically treating livestock and poultry wastewater relates to an apparatus for biologically treating wastewater and solves the following problems: in present biological treatment of the livestock and poultry wastewater, the treatment of the livestock and poultry wastewater by using an anaerobic technique does not achieve good deamination and denitrification effect, the treatment of the livestock and poultry wastewater by using an aerobic technique requires great investment and high operation cost, and the treatment of the livestock and poultry wastewater by using an anaerobic-aerobic technique has the disadvantages of large area occupation, long process route and high capital expenditure. Anaerobic granular sludge is arranged in an upper cylinder body of a lower anaerobic reaction cylinder body, a triphase separator is arranged in an upper anaerobic reaction cylinder body, a shielded box and an aerobic box are arranged on an upper end face of the upper anaerobic reaction cylinder body, a tapered cavity body is arranged in the shielded box, a floater is arranged in the tapered cavity body, a gas distributing device is arranged on a motherboard of the aerobic box, and reactant is arranged in the aerobic box. The invention has the advantages of good effect in removing ammonia and nitrogen, small investment, low operation cost, small device occupation area, simple process flow, low capital expenditure, simple structure, etc.