The present invention provides a video image decoding method, and the method comprises the steps: determining the size of an affine movement compensation sub-image block in an affine image block according to the motion vector differences, motion vector accuracy, the distance between control points in the affine image block, and the size of the affine image block, wherein the size includes a lengthin the horizontal direction and a length in the vertical direction so that the length of the affine image block in the horizontal / vertical direction is integer multiples of the length of an affine motion compensation sub-image block; finally, decoding the affine image block according to the size of the affine motion compensation sub-image block. The method can adaptively adjust the size of the affine motion compensation sub-image block to the optimal size according to the attribute of the affine image block itself, thereby guaranteeing the quality of the decoding, reducing the decoding complexity and effectively improving the decoding efficiency.