In order to survive severe global competition in manufacturing industries, there is a growing importance in manufacturing systems' efficient operation. To maintain the efficient operation, continuous improvement activities, Kaizen activities, are necessary. The current Kaizen activities solve only individual problems of machines and workplaces, but these activities cannot always bring the best solution as the whole manufacturing system performance. From the viewpoint of the system performance, it is necessary to use manufacturing system simulation to determine the order of priority of Kaizen ideas. This study proposes the integration system that is able to update the simulation model using the data of Manufacturing Execution System (MES) in order to make the simulation model efficiently. To realize the integration between MES and simulator, XML is used to define the format of the common data. For practical use, the user interface shows the values of the exchanged data and the original data, so that the user can check the values of both exchanged data and the original one, and choose which to refer to. To confirm the effectiveness of this simulation environment, a test case is tried out. This study is done as the MISSION project funded by IMS program.