A simplicity HDTV video decoding method includes the steps of: variable-length-decoding an input image signal, and dividing it into a luminance signal, a color difference signal and a motion vector; reverse-quantizing each of the luminance and color difference signals received, and reverse-converting it to be half in horizontal size; and storing each of the reverse-converted luminance and color difference signals in the unit of frames, and motion-compensating it by using the motion vector, thus reducing the memory and other logic circuits in half by motion-compensating each of the luminance and color difference signals, generated in parallel by an 8×4 IDCT.