A method for decoding a bitstream for a video signal, the method performed by a decoding apparatus and comprising: obtaining a plurality of prediction blocks from a coding block; obtaining merge flag information of a current prediction block of the plurality of prediction blocks from the bitstream, the merge flag information indicating whether the current prediction block is coded in a merge mode; obtaining merge index information of the current prediction block from the bitstream, the merge index information specifying a merging candidate to be merged with the current prediction block from among merging candidates including spatial and temporal neighboring blocks of the current prediction block; deriving prediction information of the current prediction block based on the merging candidates and the merge index information, the prediction information including motion vector information and reference index information; and performing an inter prediction for the current prediction block based on the prediction information of the current prediction block, wherein, based on the coding block 2Nx2N being partitioned into a left Nx2N prediction block and a right Nx2N prediction block and the current prediction block being the right Nx2N prediction block of the coding block, the left Nx2N prediction block of the coding block is excluded from the merging candidates, and wherein, based on the coding block 2Nx2N being partitioned into an upper 2NxN prediction block and a lower 2NxN prediction block and the current prediction block being the lower 2NxN prediction block of the coding block, the upper 2NxN prediction block of the coding block is excluded from the merging candidates. obtaining a plurality of prediction blocks from a coding block; obtaining merge flag information of a current prediction block of the plurality of prediction blocks from the bitstream, the merge flag information indicating whether the current prediction block is coded in a merge mode; obtaining merge index information of the current prediction block from the bitstream, the merge index information specifying a merging candidate to be merged with the current prediction block from among merging candidates including spatial and temporal neighboring blocks of the current prediction block; deriving prediction information of the current prediction block based on the merging candidates and the merge index information, the prediction information including motion vector information and reference index information; and performing an inter prediction for the current prediction block based on the prediction information of the current prediction block, wherein, based on the coding block 2Nx2N being partitioned into a left Nx2N prediction block and a right Nx2N prediction block and the current prediction block being the right Nx2N prediction block of the coding block, the left Nx2N prediction block of the coding block is excluded from the merging candidates, and wherein, based on the coding block 2Nx2N being partitioned into an upper 2NxN prediction block and a lower 2NxN prediction block and the current prediction block being the lower 2NxN prediction block of the coding block, the upper 2NxN prediction block of the coding block is excluded from the merging candidates.