The clomazone herbicide wastewater was treated using a combined technology composed of electrochemical catalytic oxidation and biological contact degradation. A new type of electrochemical reactor was fabricated and a Ti/SnO2 electrode was chosen as the anode in electrochemical-oxidation reactor and stainless steel as the cathode. Ceramic rings loaded with SnO2 were used as three-dimensional electrodes forming a packed bed. The operation parameters that might influence the degradation of organic contaminants in the clomazone wastewater were optimized. When the cell voltage was set at 30 V and the volume of particle electrodes was designed as two-thirds of the volume of the total reactor bed, the chemical oxygen demand (COD) removal rate could reach 82% after 120 min electrolysis, and the ratio of biochemical oxygen demand (BOD)/COD of wastewater increased from 0.12 to 0.38. After 12 h degradation with biological contact oxidation, the total COD removal rate of the combined technology reached 95%, and effluent COD was below 120 mg/L. The results demonstrated that this electrocatalytic oxidation method can be used as a pretreatment for refractory organic wastewater before biological treatment.