Abstract: The organic pollutants in oilfield wastewater are difficult to degrade. It's hard to decrease COD to below 50 mg/L by using common methods. Fenton Reagent is used as oxidant to treat COD in oilfield wastewater. Temperature, pH, reaction time, the concentration of H₂O₂, and the Fe²⁺ concentration are experimented to determine their effects on removal of COD in oilfield water. The best single factor has been determined in the experiment. The Orthogonal experiment shows there are four combined conditions which can be satisfied to decrease COD value to below 50 mg/L. At last, the practical application of this method in oilfield wastewater treatment is discussed.