Abstract: Considering the poor biodegradability of the refractory pharmaceutical park tail water, activated sludge adsorption, O₃ oxidation and adsorption of activated sludge coupled with O₃ were separately used to pre-treat pharmaceutical tail water, and the test parameters were optimized. The results showed that separate activated sludge adsorption method had a certain ability to remove organic matter, but it could not effectively improve the biodegradability of the wastewater; both the COD_Cr removal efficiency and the biodegradability of wastewater were greatly improved by O₃ oxidation and adsorption of activated sludge coupled with O₃. It was verified that activated sludge coupled with O₃ process was an effective pretreatment technology, the COD_Cr removal efficiency could reach 37.90%, and the biodegradability was greatly improved, with BOD₅/COD_Cr increasing from 0.020 to 0.141, and its processing cost is more economical.