To study the regularity of residual change of florfenicol in Beijing fatty chicken, 153 healthy Beijing fatty chickens were randomly divided into 4 groups, 40 cocks and 40 hens in the treatment group, 40 cocks and 33 hens in the control group (7 hens died during the experiment). The daily dose of the drug for treatment group was 21.6mg/(kg·bw) for cocks and 21.4mg/(kg·bw) for hens. The treatment group was fed with florfenicol powder orally for 5 consecutive days. The control group fed without any antibacterial drug was kept under the same condition as the treatment group.At 2.5h-21d after drug withdrawal, 6 cocks (4 in the treatment group and 2 in the control group) and 6 hens (4 in the treatment group and 2 in the control group) were slaughtered. The samples of muscle, kidney and liver were collected, respectively. The residues of florfenicol and florfenicol-amine in tissues were determined by ultra-performance liquid chromatography-tandem mass spectrometry, and the withdrawal period was calculated by WT 1.4 software. The results showed that the average residue of florfenicol and florfenicol-amine with the value of (881.88±278.90)μg/kg in liver was the highest, which was followed by values in kidney and muscle tissue. And the drug was eliminated slowly. In order to ensure food safety, it recommended that the withdrawal period of florfenicol in Beijing fatty chicken should be no less than 12 days.