Recently, Internet has been used widely. Many scholar digital libraries have also followed this trend and grown up quickly. However, information in these digital libraries is complex and huge. Users are difficult to discover papers they need; instead, they often get lost in the information. When they search these digital libraries, they are also limited to the documents which are embodied in these digital libraries, and can not locate important papers in other journals. Citation Analysis has been used in many areas and it is used in this research to build an expert system. Further, we will discover important papers which can represent these research areas. We called these papers as ¡§Key Papers¡¨. A citation can be classified by its relation as ¡§Direct Citation¡¨ and ¡§Indirect Citation¡¨. Many researchers showed that indirect citations held influence, but in the past they just used direct citations to calculate importance and neglected indirect citations. This research combined direct and indirect relations into one index, and used this index to build the expert system. In addition, we provided a visualization of papers¡¦ citation relations, and helped users to find key papers in their research areas. In order to test our system, we collected the top six journals in MIS, totally 7579 papers, and extracted 129114 citations from these papers. The result showed no differences between direct and indirect citations. However, key papers that didn¡¦t belong to these journals could be discovered, and using top three journals could obtain the same result as found in using top six journals.