Objective： Taking prednisone as the control， to observe the clinical effect of Yajia Formula in the treatment of severe subacute thyroiditis （SAT）.,Methods,2,A total of 76 severe SAT patients with heat-toxic congestion and blood-heat stagnation type were selected and randomly divided into the treatment group and control group， 38 cases in each group. The patients in the treatment group were orally treated with Yajia Formula granules and the patients in the control group were orally treated with prednisone acetate tablets， with a course of 8 weeks. The clinical effect and the Chinese medical syndrome effect were evaluated in the two groups. The relief time and disappearance time of fever and thyroid pain and the improvement of thyroid ultrasonography were compared between the two groups. The incidences of adverse reactions were compared between the two groups. Follow-up for 3 months after the end of the treatment course， the recurrence rates of the two groups were compared.,Results,2,In the course of the research， 3 patients in the treatment group and 3 patients in the control group were eliminated or shed off， finally 35 patients in the treatment group and 35 patients in the control group were included in the statistical analysis. ①After treatment， the total clinical effective rates of the treatment group and the control group were 91.43% and 85.71% respectively， and the effect of the treatment group was better than that of the control group（,P,<,0.05）； after treatment， the total effective rates on Chinese medical syndrome in the treatment group and the control group were 91.43% and 62.86% respectively， and the effect on Chinese medical syndrome in the treatment group was better than that in the control group （,P,<,0.05）. ②The relief time and disappearance time of fever and thyroid pain in the treatment group was significantly longer than that in the control group （,P,<,0.05）. ③After treatment， the condition of thyroid ultrasonography in the two groups was significantly improved compared with that before treatment （,P,<,0.05）， but there was no statistical difference between the two groups （,P,>,0.05）. ④In the course of the research， the incidences of adverse reactions in the treatment group and the control group were 0% and 22.86% respectively， and the incidence of adverse reactions in the treatment group was significantly lower than that in the control group （,P,<,0.01）. ⑤The recurrence rates of the treatment group and the control group were 0% and 36.67% respectively， and the recurrence rate of the treatment group was significantly lower than that of the control group （,P,<,0.01）.,Conclusion,2,Yajia Formula has better clinical effect in treating severe SAT patients with heat-toxic congestion and blood-heat stagnation type， and can improve the Chinese medical syndrome and the hypoechoic condition of thyroid ultrasonography with less adverse reactions and lower recurrence rate.