1. A temporal error concealment (TEC) method, for generating a replacement macroblock (macroblock) for filling up a missing macroblock according to a correct image data of a previous image frame and a part of correct image data of a current image frame, thus concealing a negative affection caused by the missing macroblock to the current frame, wherein each of the previous frame and the current frame comprises a plurality of macroblocks, and each of the macroblocks comprises a plurality of pixels, and an image data of the missing macroblock is incorrect, the TEC method comprising: dividing the missing macroblock into a plurality of N×N pixel missing blocks, wherein N is a positive integer; dividing a plurality of N-pixel-wide boundary macroblocks surrounding the missing macroblock into a plurality of N×N pixel boundary blocks; constructing an optimal regression (OR) plane by a multiple polynomial regression equation according to motion vectors (motion vectors) of the boundary blocks surrounding the missing macroblock; predicting a spatial motion vector of the missing blocks, according to the OR plane; taking a motion vector of a macroblock in the previous frame at a position corresponding to the missing macroblock as a temporal motion vector; selecting a spatial motion vector or a temporal motion vector having a least adjacent external boundary matching error (AEBME) as a candidate motion vector, according to a boundary matching algorithm (BMA); dividing the missing macroblock into a plurality of sub-macroblocks (sub-macroblocks) having less pixels, according to a motion field and a Laplacian probability distribution of the candidate motion vector; comparing an adaptive search range (ASR) with a dynamic threshold value (DT a ), following a spiral scanning path starting from a starting point which is an average motion vector of the candidate motion vector and spirally spreading outward, along all motion vectors of the boundary blocks, wherein if the ASR is equal to or smaller than the threshold value, it indicates that the desired motion vector has been obtained and the search is terminated, or otherwise if all of the ASR are greater than the threshold value, one having a least ASR among the motion vectors is selected as the desired motion vector; and moving the replacement macroblock to the position of the missing macroblock according to the motion vector for filling up the image data of the missing macroblock, and thus concealing a negative affection caused by the missing macroblock to the entire image frame.