The invention discloses a top block structure applied to a braking clamp lever mechanism. The top block structure is provided with a top block body, the top block body is provided with two coaxial connecting shafts, the connecting shafts and the top block body are installed, connected or manufactured into a whole, the connecting shafts are located on the outer wall of the top block body, the top block body is provided with a radial location hole, and the location hole is in threaded connection with a limiting screw. A mounting hole is formed in the top block body, a fixed plug is installed in the mounting hole, a circumferential limiting groove is formed in the peripheral wall of the fixed plug, the front end face of the fixed plug is provided with a counter bore, and a pressing block is installed in the counter bore. After the top block structure is applied to the braking clamp lever mechanism, the maximal contact area of the pressing block of the top block structure and an output shaft of a brake cylinder can be maintained all the time, braking force transmission efficiency is effectively improved, in case of malfunction, manually-operated alleviation can be achieved by adjusting the fixed plug in the top block structure, operation is simple, after the pressing block is worn, it only needs to replace the pressing block, and maintenance cost is low.