To improve the efficiency of petrochemical wastewater treatment, a hybrid system with both attached and suspended biomass was proposed to replace the existing biofilm process. According to the performances of the hybrid system, the optimal suspended biomass concentration in the tank was determined around 1000 mg/L. When the average influent COD and NH4+-N concentration were 395.7 mg/L and 13.5 mg/L, the according removal efficiencies of the hybrid system were up to 84% and 69%, compared to 74% and 20% when operated with the biofilm system. The GC-MS analysis showed that both the amounts and types of refractory organics in the effluent of hybrid system were greatly reduced when compared with those of the previous biofilm process. The foaming problem was also resolved along with the enhanced pollutants removal efficiency. The hybrid process was an economic and feasible alternative for petrochemical wastewater treatment, which ensured carbonaceous oxidation, nitrification and decomposition of refractory substances.