Abstract ： Objective ： To observe the clinical effect of Siwei Daicha Decoction as adjuvant therapy for type 2 diabetes mellitus （T2DM） with syndrome of excessive heat damaging fluids. Methods： Seventy patients diagnosed with T2DM with syndrome of excessive heat damaging fluids at Huzhou Nanxun Hospital of Traditional Chinese Medicine from May 2022 to April 2024 were randomly divided into the observation group and the control group by the computer randomization， with 35 cases in each group. The control group received Metformin Hydrochloride Sustained-Release Tablets，while the observation group received additional Siwei Daicha Decoction based on the treatment of the control group. Both groups were treated for eight weeks. The following indexes were compared between the two groups before and after treatment： blood glucose indexes [fasting blood glucose （FBG）， 2-hour postprandial blood glucose （P2hBG）， glycated hemoglobin （HbA1c）]， traditional Chinese medicine （TCM） syndrome scores （constant thirst and excessive drinking，dry mouth and tongue，frequent urination with large volume，vexation and sweating），lipid indexes [total cholesterol （TC）， triglycerides （TG）， high-density lipoprotein cholesterol （HDL-C）， low-density lipoprotein cholesterol （LDL-C）]， and adverse drug reaction incidence rates. Results： After treatment， the levels of FBG， P2hBG， and HbA1c in both groups were decreased when compared with those before treatment （P＜0.05）， and the levels of FBG， P2hBG， and HbA1c in the observation group were lower than those in the control group （P＜0.05）. After treatment，the control group showed no statistically significant differences in the scores of dry mouth and tongue， vexation and sweating when compared with those before treatment （P＞0.05）， but the scores of constant thirst and excessive drinking， and frequent urination with large volume were decreased when compared with those before treatment （P＜0.05）；in the observation group，the scores of constant thirst and excessive drinking，dry mouth and tongue，frequent urination with large volume，and vexation and sweating were all reduced when compared with those before treatment and were lower than those in the control group （P＜0.05）. After treatment，there was no statistically significant difference in the levels of the TC，TG，HDL-C and LDL-C in the control group or in the levels of HDL-C and LDL-C in the observation group when respectively compared with those before treatment （P＞0.05）. However，the levels of TC and TG in the observation group were decreased when compared with those before treatment and were lower than those in the control group （P＜0.05）. The incidence of adverse drug reactions was 13.33% （6/35） in the observation group and 11.11% （5/35） in the control group， there being no significant difference between the two groups（ P＞0.05）. Conclusion：The adjunctive use of Siwei Daicha Decoction in the treatment of T2DM with excessive heat damaging fluids syndrome can enhance glycemic control，improve TCM syndrome manifestations and lipid indexes， with excellent safety.