A video decoding method according to the present invention may comprise: a step for dividing a coding block into a first partition and a second partition; a step for deriving a merge candidate list for the coding block; a step for determining a first merge candidate and a second merge candidate by using the merge candidate list; a step for deriving a first prediction sample and a second prediction sample on the basis of first motion information on the first merge candidate and second motion information on the second merge candidate; and a step for obtaining a third prediction sample for the coding block on the basis of the first prediction sample and the second prediction sample.