Whether 12mm of portal vein of liver is normal should be analyzed specifically, if it is 12mm of portal vein trunk, it is normal, if it is the inner diameter of non-portal vein trunk, it is not normal. 1. The portal vein trunk of the liver in normal adults is 6-13mm, and a few people can reach 15mm. 12mm internal diameter of the portal vein trunk under ultrasound display is generally considered normal, but we should be vigilant and follow up on time. 2. If the internal diameter of the main trunk of the non-portal vein reaches 12mm, then it cannot be considered normal, and the possibility of portal hypertension cannot be ruled out, and CT of the liver, portal venography and other examinations should be performed to clarify whether there is liver disease. Therefore, when the inner diameter of portal vein reaches 12mm, we should consult the attending doctor in time to clarify whether it is the main trunk or other branches, and to understand the specific situation of liver and portal vein pressure to avoid the development of the disease.