The inconsistency between the radar image information and electronic chart information in the high latitudes can result in much difficulty on the identification of marks, which will be dangerous to the ship's navigation. By analyzing the characteristics of the projection methods of the high-latitude sea area charts, we discuss the causes for the errors of the radar image and superimposed ECDIS information. This thesis puts forward the method of subdivision of longitude in the weft to correct the Mercator projection distortion, and therefore we can get the Mercator projection which is able to meet any predetermined accuracy requirements. Based on GPS coordinates value, radar real-time location information is changed into the screen coordinates through a coordinate transformation, and we can position radar center position on the ECDIS chart accurately. In this way, we can realize the real-time, rapid, precise overlay display of radar echo and ECDIS chart.