The invention provides a motion prediction method. First, a plurality of candidate units corresponding to a current unit of a current frame is determined A plurality of motion vectors of the candidate units is then obtained. A plurality of temporal scaling factors of the candidate units is then calculated according to a plurality of temporal distances between a plurality of reference frames of the motion vectors and the current frame. The motion vectors of the candidate units are then scaled according to the temporal scaling factors to obtain a plurality of scaled motion vectors. Finally, a motion vector predictor for motion prediction of the current unit is then selected from the candidate units according to the scaled motion vectors.