The Predicated No Effect Concentration (PNEC)of norfloxacin in the freshwater sediment was derived by the Species Sensitivity Distributions(SSDs) method and distribution equation model with collected and calculated chronic toxicity data. Those data collected were fitted in 5 different models by SSDs method,the model of log-normal was fitted best. The PNEC of norfloxacin in freshwater sediment was 1 612.82 ng/g. Also, ecological risk assessment of existing research of the sediment in different freshwater areas were conducted by risk entropy. The results show that, in China, the ecological risks of known statistics of the concentration of NFLX in sediment, were between medium and low and some sample sites showed high risk, which probably had potential hazard to freshwater ecology system.