In Postal logistics, the efficient design and operation of transportation network is very important issue. But, it is hard to operate the postal transportation network flexibly according to the change of mail volume. In Korea post, a transportation plan is pre-determined and the transportation of mail is performed through the routes in the plan. When the routes cannot transport all mail, temporary vehicles are used. In the postal transportation, it is important to make a good transportation plan and to manage the plan efficiently. But the change of transportation plan is not a simple work because hundreds of vehicles and persons are related to the plan. So, a methodology to check the effect of the change of the transportation plan in advance is required. In this paper, we develop a simulation model to evaluate the performance of a postal transportation plan. We implement the simulation model and develop an information system including user interface for managing data and simulation results. We apply our simulation model and system to the real change of transportation plan.