Taking Procambarus clarkii as the research object，they were randomly divided into 4 groups with 60 tails in each group.They were fed with basic feed coated with florfenicol of 0 （C0），10 （C10），20 （C20） and 30 mg/kg （C30） for 20 d followed by a period of feeding without florfenicol for 15 days to evaluate the elimination pattern.The activities of hepatopancreatic phase Ⅰ drug metabolizing enzymes 7-ethoxycoumarin-O-deethylase （ECOD），7-ethoxyisophenoxazolone-O-deethylase （EROD），aniline-4-hydroxylase （AH），erythromycin-N-demethylase （ERND），aminopyrine-N-demethylase （AND），phase Ⅱ drug metabolizing enzymes glutathione-S-transferase （GST），sulfotransferase （SULT），and uridine diphosphate glucuronosyltransferase （UGT） were measured.Expression levels of cytochrome P450 （CYP450），GST，heat shock protein 70 （HSP70） and metallothionein （MT） mRNA were measured.The results showed that florfenicol significantly reduced phase Ⅰ metabolic enzymes activities but increase phase Ⅱ metabolic enzymes activities （P<0.05）.The results of gene expression showed that florfenicol could up-regulate CYP450 gene expression.Florfenicol of 10 mg/kg up-regulated GST gene expression，but 20 mg/kg and 30 mg/kg florfenicol could inhibit GST gene expression.The inconsistency between gene expression and enzyme activity showed that there was no inevitable relationship between gene transcription and protein synthesis.The results suggest that 10 mg/kg florfenicol maintains the homeostasis of the body by inducing the expression of HSP70，MT and other genes，but high-dose florfenicol is beyond the tolerance of the body and causes damages to the organism.The results of elimination test showed that after 15 days of elimination，except GST enzyme activity，the activities of other drug metabolism enzymes in C10 group returned to normal level，and the expression levels of four drug metabolism genes also returned to normal level.For the sake of safety，when feeding P. clarkii with florfenicol，the recommended dose is 10 mg/kg，which is not only conducive to give full play to the efficacy without being excluded from the body prematurely，but also avoid the body damage and accumulation caused by too high dose of florfenicol.