The invention provides a belt tightener, and belongs to the technical field of machines. The problems that an existing tightener is poor in non-return buckling strength and prone to deforming and failing after long time, a pull rope will loosen, and the effect and the stability after tightening are poor are solved. The belt tightener comprises a support and a reel; the support is provided with two opposite side plates, shaft holes are formed in the two side plates, ratchet wheel portions are arranged at the two ends of the reel, are located in the corresponding shaft holes and can rotate in the shaft holes along with the reel, a sinking-in clamping opening is formed in the inner wall of the upper side of each shaft hole, and under the external force effect of the ratchet wheel portions, the ratchet wheel portions can be eccentrically moved to enable one ratchet to be clamped in the corresponding clamping opening. The ratchet wheel portions of the belt tightener are arranged in the shaft holes, after tightening, under the tightening force effect, the ratchet wheel portions can be eccentrically moved to be clamped in the clamping openings, the clamping openings are formed in the support, the whole strength is large, deformation and failures cannot appear even after long time, and the effect and the stability after tightening are good.