The utility model relates to the technique of oil drilling and production equipment, in particular to a telescopic mechanism of a headframe which is suitable for three cased headframes which are formed by a headframe upper body, a headframe middle body and a headframe lower body, is provided with a pair of telescopic hydraulic cylinders which synchronously work and are mounted between the hearframe lower body and the headframe middle body, and is further provided with a cable wire-pulley lifting mechanism which is formed by a pulley which is mounted on the headframe middle body and cable wires which are around the rear both ends of the pulley and are respectively mounted on the headframe lower body and the headframe upper body. Since the telescopic mechanism is provided with the headframe middle body which drives the cable wire-pulley lifting mechanism to work through the protrusion and the contraction of the telescopic hydraulic cylinders, thereby simultaneously driving the headframe upper body to extend out and retract. The utility model has the advantages of simple structure, low cost and high telescopic operation cost.