In this paper, a fitted upwind difference scheme has been presented for solvingsingularly perturbed differential-difference equations with negative shift. First, the singularlyperturbed differential-difference equation has been replaced by an asymptotically equivalentsingular perturbation problem. Then, a fitting factor is introduced into upwind finite differencescheme and obtained from the theory of singular perturbations. Then, a three term recurrencerelation is obtained. The resulted tri diagonal system has been solved by Discrete InvariantImbedding Algorithm. The efficiency of the method has been demonstrated by implementing onseveral model examples by taking different values for the delay and the perturbation parameters.