The work aims to design a fully flexible automatic packaging production line for bag packaging. The bag packaging production line was divided into silo, quantitative feeding device, unwinding device of packaging material, vacuum heat-sealing device, segmentation device, unreeling device, automatic counter, PLC program control and human-machine interface. Flexible design was conducted for all the devices. An automatic production line was finally worked out. The average mean time between failures 1164 h was calculated by reliability prediction. It showed that the production line could meet the actual production demand. In conclusion, the production line has a strong flexibility and frugality. It is of great significance to shorten the production cycle, reduce production costs, rapidly response to customer demand, and achieve agile production.