A dental floss device, comprising a floss holder and a floss tensioner； the floss holder comprising a head portion (11) and a holding portion (14)； the head portion (11) comprising four arm portions (111A, 111B, 112A, 112B)； whereby the floss tensioner adjusts tension of the dental floss by adjusting rotation of the head portion (11) comprising the first gear (13) relative to the holding portion (14) comprising the second gear (141), by rotating a third gear in the holding portion (14) which is coupled with a floss-winding post (190), or by moving the floss-winding post (190) within a trough (200) in the holding portion (14). The dental floss device can tension the dental floss, and clean the gap between teeth as well as the gum.
