This study aims to construct a mixed culture system of Oocystis and diation Phaeodactylum tricornutum,and evaluate its potential for removing nitrogen and phosphorus as well as treating antibiotic-containing aquaculture tailwater. The nitrogen and phosphorus removal capacity was evaluated by monitoring water quality parameters(NH -N,NO -N,NO -N,PO- -P ,and CDO) ,assessing carbon capture capacity by monitoring microalgae growth,and exploring the stress response of microalgae to antibiotics by monitoring the chlorophyll a content and antioxidant enzyme activity. Results showed that the mixed algae system achieved a 100% removal rate of ammonia nitrogen. The concentrations after treatment of nitrate nitrogen, nitrite nitrogen,total nitrogen,total phosphorus,and chemical oxygen demand were 13. 50± 1. 17 mg/L,0. 20± 0. 01 mg/L,15. 09 ± 1. 14 mg/L,0. 71 ± 0. 03 mg/L,and 31. 57 ± 2. 51 mg/L,respectively,with corresponding removal efficiencies of 86. 03% , 67. 33% ,86. 13% ,94. 87% ,and 50. 60%. The concentration of CIP was 4. 52±0. 45 mg/L,with a removal efficiency of 90. 95%.The carbon capture rate(CO2 -equivalent) of Oocystis reached its peak with 0. 47 g/(L ·d) during the logarithmic growth phase. Microalgae enhanced their antioxidant capacity by increasing the activities of CAT and POD. This study indicates that the mixed algae culture system has a positive effect on nitrogen and phosphorus removal,as well as ciprofloxacin removal. It provides new perspectives for the resource utilization of aquaculture tailwater and important practical application.