OBJECTIVE： To establish the method for detect the improvement effects of triptolide （TP） on joint injury in rheumatoid arthritis （RA） model rats. METHODS： Totally 18 SD rats were randomly divided into normal control group （0.9％ Sodium chloride solution）， model group （0.9％ Sodium chloride solution） and TP group （0.5 mg/kg）， with 6 rats in each group. Model group and TP group were given incomplete Freund adjuvant-chicken type II collagen （1 ∶ 1，V/V） 0.1 mL subcutaneously via tail for initial immunity， and 7 d later given secondary immunity to established RA model. After modeling， they were given relevant medicine intravenously via tail vein； normal control group and model group were given constant volume of 0.9％ Sodium chloride solution， every 2 d， for consecutive 30 d. Body weights of rats were weighed before medication， 5， 10， 15， 20， 25， 30 d after medication. Arthritis indexes of rats were scored before medication， 3， 6， 9， 12， 15， 18， 21， 24， 27， 30 d after medication. Positron emission computed tomography （PET）/tomography （CT） were used to scan the joint of rats 6， 18， and 30 d after administration. 18F-FDG 500 μCi was injected into the tail vein 50 min before scanning. The filtered back projection image reconstruction algorithm was adopted for PET imaging. CT scanning was used for standard positioning. Inveon Research Workplace 4.2 analysis software was used to calculate the maximum standard uptake value （SUV） of lesions. RESULTS： Compared with normal control group， 15-30 d after medication， body weight of rats was decreased significantly in model group； 6-30 d after medication， arthritis index scores of rats were increased significantly； 6， 18， 30 d after medication， SUV of lesions in rats increased significantly （P＜0.05）， and the severity of arthritis in rats was aggravated and bone destruction occurred. Compared with model group， 15-30 d after medication， body weight of rats increased significantly in TP group； 21-30 d after medication， arthritis index score of rats decreased significantly； 18， 30 d after medication， SUV of lesion decreased significantly （P＜0.05）， and arthritis relieved gradually. CONCLUSIONS： 18F-FDG PET/CT imaging is an efficient method to monitor the improvement effect of TP on joint injury in RA model rats.