The invention discloses a detector for the sliding smoothness of sliding rails. The detector comprises a movement mechanism, a fixing mechanism of a lower sliding rail and a sliding smoothness detection mechanism of an upper sliding rail which are mounted on a frame plate successively from front to back. The movement mechanism moves the sliding rail to be detected to the fixing mechanism of the lower sliding rail, and fixes the sliding rail to be detected on the fixing mechanism of the lower sliding rail; a pair of force measuring mechanisms in the sliding smoothness detection mechanism of upper sliding rail move the upper sliding rail left and right to detect the thrust; and after detection, the movement mechanism dismounts the sliding rails from the fixing mechanism of the lower sliding rail. If the detected thrust value does not satisfy a predetermined value, a producer can adjust the cooperation relation between the upper sliding rail and the lower sliding rail, and thus, a user can use the sliding rails more conveniently.