The invention relates to a vertical multistage AO ecological sewage treatment system. The vertical multistage AO ecological sewage treatment system is characterized in that sewage is orderly treated by a coarse screen, a lifting pump house, a fine screen, a grit basin, a vertical multistage AO ecological tank, a cloth filter tank and a UV disinfection canal and then is discharged by a standard discharge opening, and sludge produced by the fine screen, the grit basin, the vertical multistage AO ecological tank and the standard discharge opening is transferred into a sludge storage tank, then is treated in a dehydration machine room and can be carted. The treatment system has less sludge amount (of sludge-drainage time of 20-25 years), does not produce odor, realizes thorough removal of organic matters, provides a carbon source produced in sludge stabilization for denitrification demands, reduces an external carbon source, produces water satisfying first-grade standard A or B, can be used for construction of an ecological landscape park, has the advantages of less construction investment and short construction period, can utilize waste and old or existing pits, ponds, trenches and slopes, and has a construction period of 4-6 months.