ORACLE, being powerful and complicated, is one of the most popular business database software systems. The emphasis of the study is put on the configuration connection method. The structure of ORACLE database and its communication mode between client and server are discussed, based on which the connection method between ORACLE client and server is explained by networking and process communication modes, respectively. The configurations from client side and server side under the different connection modes are described. Two solutions to connection malfunctions are given as examples.