This invention discloses an image capture device and an image synthesis method thereof. The image capture device comprises an image pickup module and a processing module. The image pickup module scans a plurality of visual angles of a scene in advance to obtain a plurality of temporary images. Each of the temporary images has a scanning focal length value. The processing module analyzes the plurality of temporary image of each of the visual angles to obtain a temporary focal length value. The processing module obtains a weighting focal length value by each temporary focal length value by using a function to control the image pickup module in order to perform a panorama image capturing process according to the weighting focal length value.