Abstract: Kelsen's theory of basic norm draws consistent and eager attention in the fields of sociological science, such as politics, law, morality, etc.This article is to focus on several important issues in the theory, including:basic norm as the tool of transforming the categories from “is” to “ought”, basic norm as non-positivistic presupposition and hypothesis, basic norm as criterion of defining legal order and identifying membership of norm, basic norm as the product of doctrine of natural law and quasi-legal positivism.In this way, the author aims to analyze the important task undertaken by basic norm and the necessary improvement of the theory of basic norm.