A fitness treadmill consists mainly of a base, two sliding rail sets and two stepping boards; each of the rail set is formed by two rails in symmetrical shape; each rail has an upper rail strip assembled on the lower rail strip and the upper and lower rail strips are implemented with one or more than one guiding section based on the stepping board moving method; whereas the two stepping boards are respectively installed with front rollers and rear rollers on the two sides for each of the stepping board set to be assembled to each sliding rail set so that the rear rollers are pressed against the upper rail strip and the front rollers are pressed against the lower rail strip for the front and rear rollers to roll along the upper and lower rails and guiding section.