In the field of aviation, it is argued the necessity of the wide area DGPS that is a new system demanding highly precise positioning accuracy. This new system has the available range of over 1000-km around the reference station, and practical use begins to be investigated. It is expected that an idea of this wide area DGPS that will be applied to the sea and the ground in the future. In this study, We paid attention to influence caused to the position accuracy of DGPS in the wide area. The influence could be made clear in the simulation and the experiment. The simulation confirmed the delay of the correction value confirmed to influence the positioning accuracy. The positioning accuracy was found a tendency to deteriorate in a ratio of 0.0031m/sec2 according to the delay time. In the observation, several medium frequency beacon DGPS station data were used. The results of these observation, the distance between the reference station and users (it is called base line length) was confirmed to influence the effect of DGPS positioning. It became clear that the position error increases in proportion to the base line length at the rate of only a few 0.12m/100km. These results show the effectiveness of the wide area DGPS.
