An embodiment of the invention provides an encoding method, a decoding method, an encoding device, a decoding device and a system for video images. The encoding method includes determining an optimum integration alternative block of a current block on the basis of the motion vector integration technology; determining a motion vector calculation mode required by a decoding side on the basis of the prediction direction of the optimum integral alternative block; rectifying the motion vector of the current block on the basis of the motion vector calculation mode; determining residual error between a predicted value and an original value of the current block on the basis of the rectified motion vector so as to encode the current block. According to the technical scheme in the embodiment, more accurate predicted value can be acquired through the rectified motion vector, smaller residual error is generated, encoding efficiency can be improved, increase of data bandwidth is avoided, and encoding quality can be improved while computing complexity is reduced.