The utility model provides a clamping ring for treads, which is applied in a mechanical type upper ring-shaped tread forming machine. The clamping ring exerts positioning pressure during the embedment of a ring-shaped tread so as to ensure the stable positioning between a tread and a tire casing, avoid the deflection of the tread and leaving of blinsters, and improve the production efficiency of tire retreading. The clamping ring mainly comprises a clamping ring body which slides along a bottom sliding seat in a reciprocating manner and a plurality of pressure plates which are arranged on the inner side of the clamping ring body and uniformly distributed along a circumference, wherein, each pressure plate is correspondingly connected with an output shaft of a cylinder; the cylinder is mounted on the clamping ring body through a cylinder seat; a side end of each pressure plate is connected with a baffle; each pressure plate and the baffle are fixedly connected through a bolt and form a 90 DEG guard bending angle; and the cylinder is provided with two side guiding slide bars.