Abstract：This paper introduces WEI Aisheng's experience in treating type 2 diabetes mellitus by "supplementing insufficiency and draining excess". Professor WEI Aisheng proposes that the principle of "supplementing insufficiency and draining excess" is taken as the key point of syndrome differentiation of type 2 diabetes mellitus. In the treatment， the excess and bias of the pathological products should be differentiated，and then the excess of phlegm-damp，static blood and constraint heat should be drained， especially phlegm-damp. Attention is paid to dispelling pathogen and making way for pathogen out. In the later stage， the lung and spleen are mainly valued， and the focus is on supplementing insufficiency of qi and yin. In clinical practice，type 2 diabetes mellitus can be divided into five types： syndrome of strong stomach，weak spleen and damp-turbidity，syndrome of qi stagnation and blood stasis，syndrome of liver constraint transforming into fire，syndrome of lung-spleen qi deficiency and damp stagnation，and syndrome of deficiency of qi and yin. The main syndrome is strong stomach，weak spleen and damp-turbidity caused by excessive water and fluids， and it is treated with modified Sanhuang Yinchen Wuling Powder. The secondary syndrome is qi stagnation，liver constraint and blood stasis caused by abnormal metabolism of water and fluids，and it is often treated with modified Danzhi Xiaoyao Powder and Xuefu Zhuyu Decoction. For patients with insufficiency of water and fluids， they are mainly with syndrome of deficiency of qi and yin， and the treatment is to use Jiangtang No.1 Prescription to supplement qi and nourish yin. In the late stage， modified Shenling Baizhu Powder is often used， and homologous Chinese medicinals are also often applied，using sweet and bland medicinals to harmonize the stomach.