This paper explores and investigates Zhang Yuansu’s treatise on the spleen and stomach in Yixue Qi Yuan(Medicine Origin)from the physiological features of spleen and stomach,syndrome differentiation and treatment of spleen and stomach diseases. Based on the achievements of many physicians and combined with his clinical experience,Zhang Yuansu founded the system of syndrome differentiation of zang-fu viscera,and had the unique thoughts on the physiological features of spleen and stomach,syndrome differentiation and treatment of spleen and stomach diseases,which formed his own spleen and stomach views. They include:the physiological view that spleen is the mother of all things and stomach is the root of human being；the syndrome differentiation view that taking the cold,heat,deficiency and excess of spleen and stomach as the principles；treatment view that treating spleen and stomach diseases by prescription formulation for dampness and basing on nourishing stomach qi. Spleen disease should eliminate dampness,and the drug selection and prescription formulation should take reinforcing and reducing methods in combination,which refer to the application of drugs with sweet or bitter flavor according to the qi movement of spleen and stomach.