The effect of phase operating time on pollutants removal efficiencies in CMICAO process was investigated at low temperature, and the relationship between DO, ORP, pH and the removal efficiencies was discussed. At 8~10 ℃, when SRT was 13 d, HRT was 16 h, sludge concentration was 2 680~3 560 mg/L and sludge return ratio was 30%, the optimal operating time of six phases were 3, 2.5, 2, 3, 2.5 and 2 h, and the concentrations of TN, ammonia, NO3--N and TP in the effluent were lower than 10.1, 1.1, 7.4 and 0.8 mg/L, respectively. When nitrification finished, pH began to rise from the fall and ORP and DO rose to flatten. When denitrification ended, ORP dropped significantly and pH rose to flatten. ORP flattened when phosphorus release finished. The DO reduction in the ex aerobic tank contributed to SND, which improves nitrogen removal efficiency and saves energy accordingly.