One of the important relationships between classes in UML is inheritance relationships. Since there are few techniques for modeling and analyzing UML, by formalizing class diagram – as important section of UML – in this paper, after converting one system to class structure in UML, we present a solution for Establishment of inheritance relationships in UML. Also we can reduce complexity of each class in the system. Then by modeling this structure by this solution it will be prepare for some goals such as verifying and validating. By using an example we show procedure of formalizing the system. After all, we come to a conclusion that formal method improves ability of analyzing and implementing a system. By improving these factors, we can get better results in other techniques such as formal... verification and validation and software testing.