Disclosed are an inter prediction method based on an affine prediction mode and a related apparatus. The method includes: obtaining a predicted pixel value of a current affine block; obtaining an LIC flag of the current affine block, where the LIC flag is used to indicate whether local illumination compensation LIC is applied to the current affine block; and when the LIC flag indicates that LIC is applied to the current affine block, updating the predicted pixel value of the current affine block based on an update coefficient for LIC, to obtain an updated predicted pixel value of the current affine block.