In this study, a combination process was developed in laboratory-scale including microwave demulsification, ozonation, and biological aerated filter (BAF) in series for the purpose of removing pollutants in oilfield wastewater with high microtoxicity. The microwave demulsification treatment removed 63.4% of oil. The ozonation treatment removed 79.3% of petroleum sulfonate, resulting in a substantial reduction of microtoxicity and great enhancement of biodegradability of the wastewater. During the following BAF process, the residual contaminants were effectively degraded by microbes. The final effluent could meet the emission standards for pollutants from petrochemical industry set by China's Environmental Protection Agency.