Increasing traffic in congested waters is going to require the traffic control all over the world. First of all, the traffic network must be designed to control the marine traffic which will be most suitable for each specified water. In Tokyo Bay, the expert group of navigation was requested to make proposals of the traffic network. They made three proposals which are different in the number of crossing point. The simulation was made to evaluate these candidate traffic networks in order to find the best solution. The GPSS model was applied for this purpose, because the simulation model of the complicated system must be simple as far as possible. In this model, the traffic network was constructed with facilities and storages in GPSS language and ships are considered to be transactions in the process. The particulars of each network were described by queue characteristics in this simulation which had been useful for the total evaluation of candidate networks as well ns for the detailed study of the specific part in the network.