The invention discloses a brake with a speed limiting function. The brake comprises a drum brake and a brake driving mechanism. The brake driving mechanism comprises a brake driving block which is arranged on the brake drum and can move in the radial direction of the brake drum, and elastic elements which are arranged between the brake driving block and the brake drum. When the rotating speed of the brake drum is lower than the preset value, the outer end of the brake driving block is constantly promoted to to be located on the inner side of a brake dividing circle under the elastic force of the elastic elements. When the rotating speed of the brake drum is higher than the set value, the brake driving block overcomes the elastic force of the elastic elements under the effect of centrifugalforce to move outwards in the radial direction, and in addition, the outer end of the brake driving block stretches out of the brake dividing circle and touches the driving frame. By means of the brake, a single-rail conveying machine can conduct brake decelerating by itself during overspeed running, and it is ensured that the single-rail conveying machine can run safely; and when the running speed of the single-rail conveying machine is too high, the centrifugal force exerted on the brake driving block is increased so that brake driving is achieved, and design is ingenious.