Two hundred and ten of overweight patients inflicted with primary diabetes mellitus who had stagnated heat of liver and stomach syndrome were recruited, which were randomly divided into 3 groups, and were given high-dosage (12g Tang-min-ling pills every time), low-dosage (6g Tang-min-ling pills every time)、placebo by 3 times every day for 12 weeks respectively. Hemoglobin A1c (HbA1c), Fasting plasma glucose (FPG)、postprandial 2 hours plasma glucose(2hPG)、syndrome、symptoms、body mass index (BMI)、waist circumference (WC) of these groups were measured and analyzed. Some safety indexes such blood and urine and stool routine examination, electrocardiogram (ECG)and liver and kidney function tests were measured and analyzed during the experiment. The treatment period is 12 week.