An electrical mold clamping apparatus of a plastic injection molding machines includes a motor unit mounted onto a link base for driving a gear at an end of a ball screw in the link base to rotate and a ball screw socket disposed at a fixed base, and the other end of the ball screw of the link base is screwed into the ball screw socket. When the motor unit drives the ball screw to rotate, the link base is displaced with the rotation of the ball screw to achieve the effect of reducing the load of the motor unit as well as the loss of energy.