Indonesia is an archipelago country, where the maritime transportation plays a major role for transporting goods from one island to the others and from out of the country to one of the islands or vice versa. In this study a subject regarding regular lnterislands ship transportation was chosen and a too for its planning was necessary to be created, especially for the following intentions : a. estimating required number of vessels on a route, b. measuring the resulted performances of: ships, ports and routes due to the various modification of the route network and its composition of the allocated ships, each ports' quay length, channel dredged level, workinghours and transhipment rate. In this study, the computer simulation model, so called INDROUTE model, was made in order to observe the dynamic behavior of the real system being studied.