Abstract: Based upon the practical experience in developing decision support systems （DSS）, this paper discusses its evolution problem from the viewpoint of structure analysis and points out that the ability to evolve is the key to the success of DSS. The paper also puts forward the new concepts of extensional structure and international structure, analyzes the shortcomings existed in the traditional first generation DSS, and gives the characteristics of the second and third generation of DSS. The existent DSS and evolutionary DSS are distinguished, and an important aspect of DSS research in the future is pointed out.