This paper describes JavaKBB, an expert systems tool, is described and the central idea of the project is to make an easy-to-use and easy-to-extend tool for building practical expert systems. It can simultaneously represent conceptual knowledge and procedural knowledge of domain; which can run on commercial operating systems such as Windows along with military domestic operating systems such as NeoKylin. This study presents a knowledge representation model of integrating frame with production rule, which defines five levels of abstraction in order to design an expert system, including knowledge primitives, knowledge units, knowledge elements, knowledge base and knowledge systems. Based on this model, JavaKBB was designed and implemented with Java language. Another important feature of JavaKBB is its capability of saving knowledge bases in XML format, thus making them potentially easy to interoperate with other knowledge bases on the Internet. Currently, JavaKBB has been used to build the Chronic Hepatitis Prophylaxis and Treatment Expert System and the Equipment Decision Support System.