The invention relates to a linear inertial piezoelectric actuator with a displacement sensing function and an actuating method. The actuator consists of a cylindrical housing, a base, a moving unit, adiamond ring, a piezoelectric stack, an inertial mass block, a permanent magnet and a proportional linear Hall sensor, wherein the bottom end of the cylindrical housing is fixedly connected with thebase; the interior of the cylindrical housing is as follows from top to bottom successively: the moving unit whose left and right ends are closely attached to a rail square groove in the casing, the diamond ring which is connected with the moving unit through an adjusting screw, the piezoelectric stack which is mounted in the diamond ring in an interference manner, the inertial mass block which isbonded under the diamond ring, the permanent magnet which is fixed to the lower surface of the inertial mass block, and the proportional linear Hall sensor which is mounted on the upper surface of the base. The linear inertial piezoelectric actuator with the displacement sensing function and the actuating method in the invention use an asymmetric sawtooth wave to drive the piezoelectric stack; actuation is performed through the principle of inertial impact; the proportional linear Hall sensor is adopted to sense the displacement in real time; the structure is compact and easy to install, theactuation is fast and accurate, the outage is locking, and the clamping force is adjustable.