The research studied enhanced treatment of sewage from discharging points of rivers by biofilm process dosing with enzyme and promotion effect of enzyme on treatment of sewage by biofilm process, and investigated the effect of the ratio of CODCr to total nitrogen (C/N) on removals of pollution indexes. The research results indicated that with the decrease of C/N, the removal rates of CODCr were stable and the removal rates of NH3-N increased, but the removal rates of TN obviously decreased in the three reactors. When C/N=5, the average removal rate of TN was higher than 30% in reactor B and C. When C/N=3, it decreased and maintained about 30%. When C/N=2, it was low and approximately 20%. When C/N=5, 3 or 2，the removal rates of CODCr, NH3-N and TN greatly increased in reactor B and C than in reactor A, which indicated that the promotion effects of the composite enzyme and the compounded enzyme on the removals of the target pollutants were favorable.