The tug boat is restricted in her maneuvering ability due to the towed barge, and tug-barge has been strongly affected by the external forces, i.e. the wind, wave, currents, and so on. Therefore, it is difficult to get the safety of tug-barge operation. It is necessary for the captain of tug boat, VTS and operation department to develope the system which can keep observing the course, speed and position of the towed barge in actual sea and prevent the marine accidents in advance. In this study, we proposed the basic method to develope the safety towing system for barge using portable GPS which was easily movable and relatively inexpensive. Then we conducted the test on the real barge. As a result, we could obtain diverse navigation data to make a safety towing work. It was noted that these data could be used for carious purposes.