A data reading method for motion estimation in an embedded system is provided. The embedded system includes an external memory device and a video encoding device, wherein the external memory device stores a first frame, and the video encoding device has an internal memory. First, a second frame is divided into M×N sub frame sets, wherein each of the sub frame sets has O×P sub frames. Then, each of the sub frame sets is selected in a calculation sequence, and the selected sub frame set is stored into the internal memory. Next, a predicted search path of each sub frame in the selected sub frame set is calculated. Thereafter; a predicted reading range is determined, wherein the predicted reading range includes the predicted search paths of the sub frames. Finally, a comparison data is read from the first frame according to the predicted reading range.