An open distributed control system (DCS), which consists of a large number of devices and a single open network interconnecting those devices, is now used in many automation areas. One critical problem of the DCS, however, is that because there is massive traffic on the network, the system integrator must carefully tune the network traffic after the construction of the system to assure its control performance. Hence, a DCS simulator is strongly needed. In our study, we propose an object-oriented design pattern approach as a uniform, rapid and accurate method of modeling and simulating a DCS. Two special design patterns are proposed: the Statechart pattern which defines classes and the state-transition execution mechanism for realizing the dynamic behavior of devices; and the device-constructor pattern which defines classes and their instantiation mechanism for realizing the structure of devices composed of many kinds of sensors and actuators. The systematic procedures from those patterns to the executable Java code of the simulation model are also discussed. Furthermore, the effectiveness of our approach was investigated through actually developing an in-house Java-based DCS simulator.