A method and a device for decoding a video signal using an adaptive separable graph-based transform. The method includes: receiving a transform index for a target block from the video signal in which the transform index indicates a graph-based transform to be applied to the target block; deriving a graph-based transform kernel corresponding to the transform index; and decoding the target block based on the graph-based transform kernel. The device includes: a parsing unit configured to receive a transform index for a target block from the video signal; and an inverse-transform unit configured to derive a graph-based transform kernel corresponding to the transform index and decode the target block based on the graph-based transform kernel.