An analysis method for a regional image is disclosed for an image datum from a C-arm device. The analysis method includes: providing an indication module, reading the image datum, selecting a plurality of ROIs (Regions of Interest), calculating an average brightness of each of the ROIs, searching every of the steel ball image data, comparing each of the steel ball image data and analyzing each of the steel ball image data. By individually analyzing the regional image datum, the brighter or darker image signal can be excluded so that it can improve precision during searching the steel ball image data. Moreover, it is also more effective for comparing an image profile of the steel ball image datum with a real profile of the steel ball of the indication module. Thus, the steel ball image can be readily defined by its correspondence with the steel ball of the indication module.