The invention provide an anaerobic ammonia oxidation-based low-carbon nitrogen ratio urban sewage denitrification system and treatment process. The system comprises a biological adsorption unit, an anaerobic ammonia oxidation unit, a nitrosation unit, a membrane technology unit and an anaerobic digestion unit, wherein the biological adsorption unit comprises an aeration tank and a settling pond; the aeration tank is connected with the settling pond; the settling pond is connected with an anaerobic ammonia oxidation tank; the anaerobic ammonia oxidation tank is connected with a nitrosation tank provided with a membrane component; the anaerobic digestion unit is an independent sludge treatment unit. The system is short in process flow, short in system startup time, stable and high-efficiency in denitrification performance, standard reach of effluent total nitrogen, low in operating energy consumption and material consumption and low in residual sludge yield. Organic matters in the urban sewage are subjected to biological adsorption removal by utilizing biological adsorption, sludge which is discharged through biological adsorption and is enriched in organic matters is subjected to medium-temperature anaerobic digestion treatment to produce biogas to be used for heating and heat preservation of the medium-temperature anaerobic digestion tank and the low-temperature anaerobic ammonia oxidation tank, the organic matters in the urban sewage can be recycled, and the operating energy consumption of the process is further reduced.