1. A method for face detection using face region location and size predictions, applicable to a computer system, said method comprising the steps of: performing face candidate region location and size predictions on an input image, which including image regionalization, region labeling and feature capturing, distance transform with constraint, and face location and size estimation, to predict at least a face location and size range for said input image; and according to said at least a predicted face location and size range, performing an adaptive face detection, further comprising: establishing face detection range, establishing window size range used for face detection, and dynamically determining at least an optimal face location for each scale of a pre-defined number of scales until at least an optimal face region being verified as face location or all scales being verified, and outputting a final face detection result.