Abstract: The mother liquor as the residual liquid was produced after the coarse salt crystallized in the three-effect evaporation system in wastewater treatment plant of Yuanba gas field, which is a high salinity wastewater containing complex components. At present, the treatment of mother liquor is facing great difficulties with the lack of mature processing technology. This study intends to carry out advanced treatment of mother liquor. After the process comparison and optimization, the mother liquor was treated by coagulation sedimentation, sulfate removal of calcium chloride, and organic compounds removal of UV+H₂O₂ co-oxidation. The effluent quality indexes were achieved by SS < 50 mg/L, sulfate radical of 4 200 mg/L and TOC of 459.25 mg/L, which can meet the requirements of influent water quality for the produced water treatment process in Yuanba gas field. Therefore, the plight of mother liquor build-up and advanced treatment would be significantly improved. The processing techniques in this study have the advantages of simple technological process and easy maintainability. To some extent, the near zero discharge of mother liquor could be achieved.