The main gearbox for Open-type Mixing Mill is supporting for opening rubber mixing machine (the mill), which is high precision and with heavy duty and tooth-flank hardened gear. For this gearbox, we adopt paralleled cylindrical gear to perform speed reducing. Through flexible coupling, the input shaft is connected to the motor shaft. Drove by the motor, reduced by parallel shafts and the gears between two output shafts and power dividing. Then the power is transmitted to rotor shaft of the roller mixing mill by the crown coupling for the two output shafts separately. In this way, the two rotor shafts of the roller mixing mill start to refine rubber.