Objective Researched the method to calculate the optimal two-stage feeding switch point of weighing packaging machines when it works. Methods Through analyzing the feeding and weighing process and the function of two-stage feeding, researched the effect of two-stage feeding switch point to the packaging speed and accuracy. Then found the range of values. Results The two-stage feeding switch point had an important impact on packaging speed and packaging accuracy, and a certain relationship. The packaging speed was maximized while ensuring the packaging accuracy through chosing the best switch point in the range of values. Conclusions Proposed a method to calculate the optimal value of two-stage switching point, while other things was the same.