Disclosed are a method for decoding a video signal and an apparatus therefor. Specifically, a method for decoding an image based on an inter-prediction mode may include: configuring a merge candidate list by using motion information of a spatial candidate and a temporal candidate adjacent to a current block; parsing a first syntax element indicating a particular candidate applied to inter-prediction of the current block among a predefined number of candidates in the merge candidate list; deriving a refined candidate by adding a motion vector offset to a motion vector of a candidate indicated by the first syntax element; and generating a prediction block of the current block by using the motion information of the refined candidate.