In order to allow user to use handheld devices accessing video information, such as downloading and playing video files, there is a need to down scale the compressed video into lower patial resolution and lower transmission bit rate. In this work, transcoding the compressed H.263 video into low patial-resolution is discused and realized. To reduce the computation cost, motion vector from the incoming video stream are resampled and reused. We propose a novel approach to refine motion vector adaptively according to the motion of every frame or every macroblock in a frame. The proposed approach can improve the video quality and reduce predictive residues of every frame, hence reduce the transmission bit rate. Implementation result suggest that the proposed approach produces better image quality and lower transmisssion bit rate than a number of previous approaches.