In Production system, there are two ; One is the JIT system, which was developed by the Toyota corporation : the other is the MRP system, which was developed in the United States. The JIT system has been proved its effectiveness for production management system by many industries, however the effectiveness of its application in non-repetitive productions is yet uncertain unlike the MRP system. There has been many efforts in comparing and analyzing the usefulness and the limitation of those production systems. Accordingly, this study has focused its simulation model using MRP and JIT.