The main causes of portal hypertension are as follows: 1, cirrhosis; 2, part of the blood stays in the portal system for a long time, because the portal pressure and the blood volume of the portal system and the vascular resistance of the portal system are positively correlated, and any cause of increased blood flow in the portal system will cause portal hypertension; 3, increased vascular resistance of the venous system will also cause portal hypertension; 4, corrosion theory; 5, mechanical friction; 6, early manifestation of hepatic encephalopathy.