Abstract: This paper puts forward a development method of ship motion simulation system that can UDP communicate on real time. This system is based on Simulink, in order to meet the need of modular and fast of ship motion simulation systems. First, set up the mathematics models of ship motion basing on the modular ideology, which include thruster model and models of wind, wave, current. Then develop the real time simulation module using S-fun function, and build into executable program, this could realize real time communication between ship motion simulation system and visual simulation system and real time communication between ship motion system and ship simulation control system. In this way, it can save time and cost when develop the simulation system. This method has been used successfully on the development of real time simulation system of some engineering ship. Keywords: Real time simulation, ship motion, simulink, UDP communication