Abstract: First studied from the linguistic and formalization view are software graphs which are widely used in the software field,and then Software Graph Languages（SGLs） are proposed in this paper.A group of basic notations in SGLs are defined,and the homomorphism and isomorphism of SGLs are studied,which are used as the basis of formal description of software graphs.Finally,the formal representation of SGLs is discussed,and the graph grammars based on symbol net are proposed so as to make graph grammars more suitable for representing SGLs.The results given can be used in designing SGL oriented tools.