Design a continuous bag opening mechanisms for automatic bag filling machine to improve the efficiency of plastic bag filling packing machine. A bag opening mechanism of plastic bag under continuous automatic filling was researched and designed based on rotary filling structure so as to realize continuous bag opening. According to the designed plastic bag tracking route, the continuous bag opening and filling structure for plastic bag was worked out. In conclusion, the design that can realize automatic continuous opening and filling will save the waiting time and improve the efficiency.