In order to treat the low-COD and unstable-SS wastewater in a domestic sewage treatment station of Zhengtong Coal Mine and meet the improved wastewater discharge standard, a process of "synchronous biological oxidation tank (SBOT) + micro flocculation filtration" was adopted to upgradethe original system. The SBOT process has the advantages of large biomass and high treatment capacity, and can simultaneously remove COD and ammonia nitrogen. The operation results show that the average concentrations of COD, TN, ammonia nitrogen, TP and SS in the effluent of the upgraded system are 12.3, 7.5, 1.1, 0.29 and, 6.2 mg/L. The effluent quality stably meets the requirements of integrated wastewater discharge standard of Yellow river basin in Shaanxi Province (DB 61/224—2018), as well as the requirements of greening irrigation, road flushing, water supply of coal preparation plants and vehicle flushing.