The invention discloses a plastic mixing device. The device comprises a machine body, a first gear and a second gear are rotatably connected to the inner wall of the machine body, the first gear and the second gear are engaged, a fan-shaped disc is fixedly connected to the side wall of the first gear, the side wall of the second gear is fixedly connected with a cam, a drive motor is fixedly connected to the inner top of the machine body, an output shaft of the drive motor is rotatably connected to the side wall of the first gear through a belt wheel, a lifting device is arranged at the inner bottom of the machine body, the upper end of the lifting device is in sliding connection with a supporting leg, a mixing bucket is arranged at the upper end of the supporting leg, a sliding groove is formed in the side wall of the mixing bucket, a guide rod is arranged in the sliding groove, and is sleeved with an L-shaped plate, the L-shaped plate is movably connected with a guide rod, and the L-shaped plate is fixedly connected to a speed adjusting device. The plastic mixing device is reasonable in structural design, easy to operate, capable of achieving sufficient mixing of plastic, and theplastic mixing effect is ensured.