This paper presents a new method of implement inference and knowledge representation in IDSS based on the product-rule by using C+[KG-*2/5]+ language. In this method, we define the structure and inference of the rule as a rule class and the specific rule as an object of the rule class to construct the knowledge base. The inference process is accomplished by using the method provided by each object of the rule class in knowledge base. The designed example shows that the new method is simple and effective.