A method for decoding a video performed by a decoding device according to the present document comprises: a step for receiving residual information for a current block; a step for parsing one sign flag for a current sub-block of the current block, wherein the one sign flag indicates whether all signs of non-zero residual coefficients of the current sub-block are the same; a step for deriving the non-zero residual coefficients on the basis of sign information for the non-zero residual coefficients when the value of the one sign flag is 1; a step for deriving residual samples on the basis of the non-zero residual coefficients; and a step for restoring a current picture on the basis of the residual samples.