Abstract: In ECDIS, in order to add radar video on chart layer simultaneously, precisely, dynamically, the gathered Radar information must be transformed, namely transform the circumference scan system to raster scan system.This paper put forward a method of proportional multiplicator which is based on trigonometric function transformation. This method solves the problem of transforming the bearing azimuth and the radial distance of an object, which is transformed to the bitmap address in the video RAM. So transformation of radar information of ECDIS is realized.