This study aims to inspect the performance of the wastewater treatment system of the Pars Oil refinery. Quantity and quality of wastewater are determined through samplings and measurements. The performance of system is evaluated considering total suspended solids, total dissolved solids, phosphate, chemical oxygen demand, biochemical oxygen demand, ammonia nitrogen, furfural, oil and pH. For precise comparing the qualitative and quantitative parameters, the wastewater entering the refinery is sampled four times from different places like boilers and from their channels, oil wastewater channels, and solvent wastewater channels. Despite some reforms that has been applied to the treatment system in order to reach the environmental standards, the system cannot treat the wastewater to the discharge standards. From the results of this research the advanced Membrane Bioreactor system for complementary refining along with optimized oil elimination system from wastewater is suggested.