An image encoding/decoding method and apparatus are provided. An image decoding method according to the present disclosure is performed by an image decoding apparatus. The image decoding method comprises constructing a merge candidate list for a current block based on a prediction mode of the current block, deriving motion information of the current block based on the merge candidate list, and generating a prediction block of the current block based on the motion information. Information on a maximum number of merge candidates included in the merge candidate list may be obtained through a sequence parameter set, and, based on the prediction mode being a subblock-based merge mode, the maximum number of merge candidates may be determined based on whether an affine mode is available for the current block.