The invention especially relates to an automatic drug mixing apparatus, belonging to the technical field of medical equipment. The automatic drug mixing apparatus comprises a tray and a control box, wherein the tray is provided with a plurality of drug bottle holding drums which are internally provided with clamping devices; the control box is internally provided with a variable-frequency motor; the bottom of the tray is provided with a transmission disk; the transmission disk is fixedly connected with the tray; the transmission shaft of the variable-frequency motor is fixedly connected with the transmission disk and deviates from the center of the transmission disk; the control box is provided with a fixed platform, and the fixed platform is provided with rolling balls; the tray is connected with the fixed platform through the rolling balls; the control box is provided with a limiting circular groove; the limiting circular groove is provided with a spiral spring; the transmission diskis located in the limiting circular groove; and the spiral spring is used for reducing the impulse of the transmission disk to the control box. The automatic drug mixing apparatus of the invention can fix drug bottles in the drug bottle holding drums and can reduce noise.