The invention provides a video encoding method, a video decoding method and a video decoding device. The video coding method comprises the following steps: when a currently to-be-coded macro block is not fully overlapped with an input image, resetting the dimension of the micro block through repeatedly reducing the horizontal dimension and the vertical dimension of the macro block to preset dimensions or repeatedly reducing the horizontal dimension and the vertical dimension of the macro block according to a preset ratio until the macro block is fully overlapped with the input image, and dividing the macro block into one or more sub-blocks when the macro block is totally in the input image; performing intraframe predication or interframe predication on each sub-block of the macro block; and through performing conversion and quantization on a residual signal which is obtained through the intraframe predication or interframe predication, and performing entropy coding on the converted and quantified residual signal.