The work aims to overcome the defects of the simple packaging metering devices of volume and weighing, and the time lag of the quantitative weighing system of the packing machine. By analyzing the working principle of the packing machine and the factors affecting its weighing precision and speed, the composite ration method and the double freedom Smith predictor were adopted to overcome the shortcomings of the traditional Smith predictor for the high precision of the parameter model. Simulation proved that the double freedom Smith prediction controlled less volatile and reached the steady state when time was 10 s. When there was external disturbance, the system overshoot was 1 time less than traditional Smith control. In conclusion, through Matlab simulation, the results show that double freedom Smith predictor can reduce the weight error of the weighing system and greatly improve the accuracy of the system output, and can significantly improve the control effect of the quantitative weighing and packing system.