The invention discloses a clamping mechanism of an injection molding machine. The clamping mechanism comprises a movable wall and a movable wall backing plate covering the movable wall; a linear motion axis and a rotation motion axis in spline fit are arranged in the movable wall; the rotation motion axis is in rotation connection with a servo motor drive; one end of the linear motion axis is in cooperative connection with a mold rotation core, and the other end is in cooperative connection with a rotating shaft connecting rod; a water jacket sleeves outside the rotating shaft connecting rod; the rear end of the water jacket cooperates with an adapter at the front of a demoulding piston rod controlled by a demoulding cylinder group; the water jacket is provided with a water inlet and a water outlet; the water inlet communicates with a water inlet pathway on the linear motion axis through an annular water inlet groove and a water inlet connection hole on the rotating shaft connecting rod; the water outlet communicates with a water outlet pathway on the linear motion axis through an annular water outlet groove and a water outlet connecting hole on the rotating shaft connecting rod; and the water inlet pathway and the water outlet pathway communicate with the rotation core. The invention has the advantages of reasonable and compact structure, good cooling effect and high machining efficiency.