Abstract: Constitutional change is to make up for the gap between social fact and constitutional norm, which is different from constitutional amending, constitutional interpretation and violation of the constitution. So, constitutional change is a kind external fact with legal validity. Constitutional change must be evaluated by the value inherent in the law. This will bring a limit of constitutional change. Constitutional change can not violate constitutional value and become unconstitutional. At the same time, constitutional change must lie in the interpretational space of constitutional text. Otherwise, we should amend the constitution to make up for the gap between social fact and constitutional norm.