A heat sink installing device includes a base, a pair of guiding poles, a slidable cover, a pair of latches and a number of auxiliary wings. The pair of guiding poles is perpendicularly mounted on the base and separated from each other. The slidable cover is slidably fitted on the pair of guiding poles and defines a pair of through holes running through two opposite side surfaces of the slidable cover. Each of the latches is mounted on the slidable cover and latched on one of the guiding poles correspondingly. The plurality of auxiliary wings are correspondingly attached on a side surface of the slidable cover around the through hole and inclined towards the center of the through hole by a distal end thereof away from the slidable cover.