The invention discloses a medicine extracting and injecting mechanical arm. The medicine extracting and injecting mechanical arm comprises an injector plunger push-pull device and an injector body clamping device. The injector body clamping device is used for clamping a cylinder of an injector and driving a syringe needle of the injector to prick into and pull out of a bottle body. The injector plunger push-pull device comprises a rack, a stepping motor, a coupler, a sliding sleeve support, a lead screw, a sliding rail, a lead screw nut, a sliding block, a magnetic grid sensor, a lead screw support, a direct current motor, a gearbox, a left clamping body, a right clamping body, a plunger push rod, a sliding block base, a pressure sensor and a sliding rod. The gearbox comprises a worm shaft frame, a worm shaft, a worm wheel, a worm wheel support, an inner gear, planet gears and a gear shaft. By means of the structure, in the aspect of intelligent preparing of the vein transfusion medicine, work of medicine extracting and injecting is achieved. The direct contact between people and the medicine can be reduced, and losses are reduced.