A video encoding and decoding method, device and system is disclosed, wherein the method includes: after using a standard encoding algorithm to complete encoding a luminance component in a current image, judging, based on refreshing images preset by an encoding device, whether there is a need to encode a chrominance component in the current image in accordance with the standard encoding algorithm or not, and encoding the corresponding chrominance component in accordance with the standard encoding algorithm if the current image is any one of the refreshing images preset by the encoding device, otherwise, not encoding the corresponding chrominance component in accordance with the standard encoding algorithm, wherein an encoding reconstruction of the chrominance component is obtained by copying a corresponding chrominance component in a reference image of luminance component, so that a finally output code stream does not comprise information of the corresponding chrominance component.