With the fuel common rail system of RT-flex diesel engine as the simulation object，studying the working principle and structural features of the fuel common rail system. The mathematical models of high pressure fuel oil pump, intermediate fuel accumulator, fuel rail ICU piston and injector is established. Analyzing the mathematical models by SIMULINK, and the mathematical models are proper. The visual simulation system of the common fuel rail system in RT-flex diesel is developed by VS2012. The visual simulation system can display the working principle and running of the common fuel rail system, and this is useful in developing marine engine simulator and training candidates.