Most rail system related simulators currently used are designed to simulate only one discipline system. This obviously assumes the other discipline systems are running regularly not being affected by the system being simulated. In this paper a multi discipline simulator is proposed and its design concept is presented. A multi discipline simulator is the simulator in which major subsystems with different technical discipline are simulated simultaneously. The advantage of the simulator is in that it makes it possible to analyze the systems behavior while other discipline system vary. With this we can identify the possible multi-discipline problems and even find their solutions. A proto type simulator has been developed using object oriented programming. Object concept was judged best suitable to model the various multi-discipline self-controlling railway subsystems. It was applied to the target system, which is under development by the Korea Railroad Research Institute. The test results shows it is very useful in designn verification. It could also be a good tool in research and development work to improve the system.