The invention belongs to the technical field of sewage treatment, and particularly relates to a micro-aerobic biological treatment process and a method thereof for treating sewage. The micro-aerobic biological treatment process and the method thereof for treating the sewage aim at solving the problems that an existing wastewater treatment technique is not complete enough, high in energy consumption, high in running expense and complicated in process, and the like. In the process, a micro-aerobic sludge bed, a filling material, a drop flow guiding groove, an oxygen-enriched water refluxing tank, a refluxing pipe, a refluxing pump, a check valve, a water inlet pipe, a settling tank, a water outlet pipe and a residual sludge discharging pipe are provided. According to the method, a micro-aerobic environment is beneficial to the mutualism among an aerobic bacterium, an anaerobic bacterium and a facultative anaerobic bacterium; these cultures metabolize a pollutant in a synergistic manner; additionally, as oxygen participates in a biochemical reaction, the oxidizing action and the reducing action in a system can occur at the same time; the anaerobic respiration, the aerobic respiration, the nitrification and the denitrification are enabled to coexist in a treatment system; the system is subjected to oxygen enrichment by a drop procedure, so as to maintain an oxygen source in the sludge bed. The process and the method are compact in layout, and have a favorable application prospect in aspects of treating wastewater; the running space and the running expense are saved.