Since the 1992 Rio de Janeiro environmental conference, the ”sustainable development” has become a core concept among the multilateral environmental legal framework. However, the legal position is uncertain of this concept. In this article, it is thought of the effective way to derive the exact legal significance of the ”sustainable development” through analysis of various sources of international law that referred to in Article 38, the statute of the ICJ.Through analysis, it is found that on one hand the ”sustainable development” do contain certain normative significance by admission of multilateral or bilateral environmental treaties, on the other hand there is a long way to go before it becomes an international customary rule from the perspective of present legal theory and precedents. On the whole, ”sustainable development” is a general concept of political environment ethic; therefore, until today it yet belongs to the field of ”soft law”.