Smaller internal diameter of common bile duct may be caused by physiological factors, or may be caused by pathological factors such as stones and inflammation. 1. Physiological factors: some patients are short in stature, and the internal diameter of the common bile duct is smaller than normal, if there are no obvious symptoms and liver function is not obvious abnormality, then regular review can be done. 2. Stones and inflammation: If there are stones or inflammation in the gallbladder or common bile duct, the stones or inflammation will constantly stimulate the bile duct wall, which will cause necrosis of the cells of the bile duct wall and scarring, resulting in thickening of the bile duct wall and narrowing of the inner diameter. 3. Tumor, lymph node compression: If there are enlarged lymph nodes or tumors around, when compressing the common bile duct, the internal diameter of common bile duct can be reduced. If you find that the common bile duct has become small, you should make a clear diagnosis to determine whether treatment is needed, and try to intervene as early as possible to avoid the development of the disease.