A video decoding method performed by a decoding apparatus, the method comprising: receiving a bitstream including video information; generating an affine motion vector predictor candidate list including affine MVP candidates for a current block; selecting one of the affine MVP candidates comprised in the affine MVP candidate list by using affine MVP candidate index information, wherein the affine MVP candidate index information is included in the video information; deriving control point motion vector predictors (CPMVPs) for respective control points (CPs) of the current block based on the selected affine MVP candidate; deriving control point motion vector differences (CPMVDs) for the respective CPs of the current block based on motion vector difference information for the respective CPs of the current block, wherein the MVD information for the respective CPs of the current block is included in the video information; deriving control point motion vectors (CPMVs) for the respective CPs of the current block based on the CPMVPs and the CPMVDs; deriving sub-block unit motion vectors of the current block based on the CPMVs for the respective CPs of the current block; deriving a predicted block based on the sub-block unit motion vectors; and reconstructing a current picture based on the predicted block, wherein the affine MVP candidates comprise inherited affine candidates, wherein the inherited affine candidates are derived based on candidate blocks coded by an affine prediction among spatial neighboring blocks of the current block, wherein the inherited affine candidates comprise a first inherited affine candidate and a second inherited affine candidate, wherein the first inherited affine candidate is derived based on a first candidate block selected from a first block group consisting of a bottom-left corner neighboring block and a left neighboring block adjacent to a top of the bottom-left corner neighboring block of the current block, wherein the first candidate block is determined based on a predefined first scan order in the first block group, and has the same reference picture as a reference picture of the current block, wherein the second inherited affine candidate is derived based on a second candidate block selected from a second block group consisting of a top-left corner neighboring block, a top-right corner neighboring block and a top neighboring block adjacent to a left of the top-right corner neighboring block of the current block, and wherein the second candidate block is determined based on a predefined second scan order in the second block group, and has the same reference picture as the reference picture of the current block. receiving a bitstream including video information; generating an affine motion vector predictor candidate list including affine MVP candidates for a current block; selecting one of the affine MVP candidates comprised in the affine MVP candidate list by using affine MVP candidate index information, wherein the affine MVP candidate index information is included in the video information; deriving control point motion vector predictors (CPMVPs) for respective control points (CPs) of the current block based on the selected affine MVP candidate; deriving control point motion vector differences (CPMVDs) for the respective CPs of the current block based on motion vector difference information for the respective CPs of the current block, wherein the MVD information for the respective CPs of the current block is included in the video information; deriving control point motion vectors (CPMVs) for the respective CPs of the current block based on the CPMVPs and the CPMVDs; deriving sub-block unit motion vectors of the current block based on the CPMVs for the respective CPs of the current block; deriving a predicted block based on the sub-block unit motion vectors; and reconstructing a current picture based on the predicted block, wherein the affine MVP candidates comprise inherited affine candidates, wherein the inherited affine candidates are derived based on candidate blocks coded by an affine prediction among spatial neighboring blocks of the current block, wherein the inherited affine candidates comprise a first inherited affine candidate and a second inherited affine candidate, wherein the first inherited affine candidate is derived based on a first candidate block selected from a first block group consisting of a bottom-left corner neighboring block and a left neighboring block adjacent to a top of the bottom-left corner neighboring block of the current block, wherein the first candidate block is determined based on a predefined first scan order in the first block group, and has the same reference picture as a reference picture of the current block, wherein the second inherited affine candidate is derived based on a second candidate block selected from a second block group consisting of a top-left corner neighboring block, a top-right corner neighboring block and a top neighboring block adjacent to a left of the top-right corner neighboring block of the current block, and wherein the second candidate block is determined based on a predefined second scan order in the second block group, and has the same reference picture as the reference picture of the current block.