In hardware design of MPEG-2 to H.264 transcoder, MPEG-2 motion vector (MV) is often reused as search center to reduce the search range for H.264 motion estimation (ME) module. But MPEG-2 MV is not always accurate search center. The common-used comparison algorithm for motion vector predictor (MVP) is hardly implemented in hardware. In this paper, we propose a MV prediction algorithm for hardware design based on smoothness of MPEG-2 MV field. Experiment results show that the proposed MV prediction method with a small search range can approach the performance of full search algorithm with a large search range. Using the proposed algorithm, the motion prediction accuracy is significantly improved compared with the method only using MPEG-2 MV, especially in sequence with fast motion and complicate background.