A prediction method and apparatus for video coding include a set of Merge candidates having an MMVD (Merge mode with motion vector differences (MVD)) candidate are generated. When the current block has a block size belonging to at least one default block size, whether a target candidate in the set of Merge candidates is bi-prediction is determined after the set of Merge candidates is generated. If the target candidate is bi-prediction: the target candidate is replaced by a uni-prediction candidate; the uni-prediction candidate is included in the set of Merge candidates to generate a modified set of Merge candidates; and current motion information associated with the current block is encoded using the modified set of Merge candidates at the video encoder side or the current motion information associated with the current block is decoded at the video decoder side using the modified set of Merge candidates.