The quinolone antibiotics (Ofloxacin, OFLX) and sulfa antibiotics (sulfamonometh-oxine, SMM, sulfamethazine, SMZ) are the two types of antibiotics with high levels in natural waters. The ecological benefits to the water environment are significant. The susceptibility of green algae to different concentrations of antibiotics was analyzed by single factor method. At the same time, the semi- inhibitory concentrations of green algae under the single and combined effects of the three antibiotics were quantitatively analyzed. Both single and combined antibiotics showed "low growth and high inhibition" for freshwater green algae, antibiotics at the concentration of ≤5μg/mL promoted the growth of algae, when >5μg/mL the growth of algae was inhibited. The semi-inhibitory concentrations of OFLX,SMM ,SMZ to C. vulgaris were 7.96 μg/mL, 6.58 μg/mL, and 8.19 μg/mL respectively, and the semi-inhibitory concentrations to S. obliquus were 6.20 μg/mL, 7.20 μg/mL, 9.89μg/mL respectively. The half-inhibitory concentration of OFLX+SMM to C. vulgaris was 8.28μg/mL, and the semi-inhibitory concentration to S. obliquus was 5.71μg/mL. The semi-inhibitory concentration of OFLX+SMM+SMZ to C. vulgaris was 10.23 μg/mL, and the semi-inhibitory concentration to S. obliquus was 7.40 μg/mL. Antibiotics showed " low growth and high inhibition " on the growth of freshwater green algae, OFLX and combined antibiotics were sensitive to S. obliquus, and SMM and SMZ were more sensitive to C. vulgaris.