A method of raster-scan search for multi-region OSD and a system using the same are provided. The multi-region OSD is to be displayed on a screen after an alpha-blending of a mixer. The method includes at least following procedures. First, a global header search is executed in the first memory module for each or a portion of a plurality of search lines so as to determine a blending region and store header addresses of OSD regions in a second memory module. Next, whether there is a dummy region at the search line is determined. In addition, an alpha value for the dummy region, a dummy data of the dummy region and the OSD data of the OSD regions at the search line are transmitted to the mixer.