Due to the implementation of the new wastewater discharge standard for oil-refining industry (GB31570-2015), the    performance of the activated sludge system was comprehensively investigated at the wastewater treatment plant in an oil refinery in western China. By monitoring the water quality for 307 days, the influent fluctuated substantially and the COD Cr, ammonia, nitrogen and petroleum in the effluent posed risks of exceeding the limits in the standard. The comparison of the effluent with the standard indicated that all the indexes except for benzene and petroleum met the standard (GB31570-2015). It is necessary to strengthen the pretreatment of the point-sources of wastewater and enhance the nitrification effect of the activated sludge process. Attention should also be paid to the removal of benzene.