The invention relates to a block brake with a cam capable of being undetached. The block brake comprises a fixed plate, a movable plate, a brake block and a brake belt. A thin boss is arranged at oneend of a pull rod and further compresses the cam onto rolling balls through steel balls, and the rolling balls are inlaid into the fixed plate. An unthreaded rod is arranged at the other end of the pull rod, and the tail end of the unthreaded rod sequentially penetrates through the fixed plate and the movable plate and is further connected with a spring tensioning device. The spring tensioning device is connected with a spring in a limiting mode, and the spring and the spring tensioning device are arranged in a groove of the brake block together. The brake block is provided with a connecting hole, and a connecting assembly is connected with the movable plate through the connecting hole. On the premise that the block brake is not detached from a traction machine, the cam of the brake cannotbe dismantled from the outside, and thus the safe reliability of the brake is improved.