An image decoding method according to the present invention comprises the steps of: receiving an MVD for a current block; deriving MVP candidates on the basis of neighboring blocks of the current block; calculating a first threshold value and a second threshold value on the basis of a first MVP candidate and a second MVP candidate included in the MVP candidates; deriving an MVP for the current block on the basis of the MVD; calculating an MV of the current block on the basis of the MVP and the MVD; and generating a prediction sample on the current block on the basis of the MV. According to the present invention, it is possible to determine at least one of the x- and y-coordinate components of an MVP on the basis of a threshold value without explicit signaling and thus reduce the amount of relevant control information, thereby improving coding efficiency. Also, it is possible to differently set the unit of resolution indicated by an MVD for each section on the basis of the threshold value and thus derive an MV over a wide area using a smaller MVD value.