This paper presented a theory of object-oriented association data model (CIM-OSA DM) for the CIM environment. After brief introduction of CIM-OSA DM , it focused on the formal definition about the fundamental concepts of the model, including object, class, and semantic association among classes. From the united point of view of object and class,it further defined the conditions of equal objects and equal classes. The definitions of sub-object and sub-class were also given formally. Some important characteristics of sub-object and sub-calss were proved.Finally,the concepts of object algebra and some operations on object were exploited.