Method and device for coding and decoding image

The embodiment of the invention provides a method and device for coding and decoding an image. The method for coding and decoding the image comprises the following steps: determining N coded units from the coded units adjacent to the unit to be coded based on a first preset rule, wherein the N coded units have the same motion prediction mode as the unit to be coded; generating an nth motion vector group by adopting a first preset algorithm according to a motion vector of the nth coded unit, wherein n contains all positive integers that are not greater than N; determining one motion vector group from the obtained N motion vector groups as an optimal motion vector group based on a second preset rule; determining a predicted pixel value for each pixel unit in the unit to be coded by adopting a second preset algorithm according to the optimal motion vector group; and coding a predicted residual value of each pixel unit and an index tag of the optimal motion vector group to obtain a code stream corresponding to the unit to be coded. By adopting the method and device provided by the embodiment of the invention, the accuracy degree of coding and decoding can be increased.