This paper introduces the selection and principle of frequency converter in dry chemical powder packing machine, which can give full play to the output torque of the motor, which is suitable for quantitative packaging control of dry white powder. Dry white powder is a powder chemical products, used for the finished product packaging dry powder quantitative packing machine feeding device, most of the use of motor drag the double spiral dosing machine. To ensure the accuracy and speed of the control system, a total of two-screw feeder large and small spiral feed, the initial state are in the stop bit. When entering the automatic operation mode, stop the large feeding motor and keep the small feeding motor running when the material weight reaches the large setting value. When the material weight reaches the final setting value, turn off the small feeding motor. Due to the dry white powder flow and the mechanical inertia of the screw feeder, coupled with the uneven material handling, quantitative dynamic accuracy of the packaging machine is difficult to control stability. Based on the above-mentioned problems, we used the frequency changer to carry on the technical transformation to the feeding device of the dry chemical powder packing machine, the form of the double helix feeder is changed to the single screw feeder form, which reduces the production cost and improves dry chemical powder packing machine.