By using parallel process of photocatalysis-biological contact oxidation, a research on the pretreatment effect of micro-polluted raw water was conducted. The result indicates that the changes of HRT and the initial concentration take significant impact on the removal of NH3-N. 60min is the best residence time for the pretreatment. Once the thickness of composite media is 120mm, the removal efficiency of CODMn may reach as much as 15.55%, while the average removal efficiency of turbidity is 20%. Since the nitration reaction consumes certain amount of alkalinity, the pH value of outlet water is lower than inlet water. When employing parallel process, biological oxidation and photocatalysis are performed and finished in the same reactor simultaneously, conducing to maintaining a moderate level of the removal of CODMn and NH3-N. All these are of reference value for its application in practical engineering projects.