Abstract: Abstract: Coal-gasification wastewater needs economical and efficient pretreatment technology to improve biodegradability, due to the high COD and biological toxicity. The sample water gets from dephenolization and ammonia stilling sections in coal gasification process of an industrial enterprise in Inner Mongolia. The experiment studies the influence of reaction conditions in Fenton oxidation step and coagulation step separately, and discusses the reaction mechanism. Under the optimum technological conditions, the COD removal rate is 80%, the chroma removal rate is 98.5% and B/C is increased from 0.17 to 0.45. Our new technology improves biodegradability obviously and reduces the pollutant load sharply for the following biological process, which will provide theoretical support for the development of coal-gasification wastewater treatment.