A set of liquid bag packaging control system design scheme was introduced, in which PLC was applied as the control core, frequency conversion motor for the implementation of components, and programmable operation display as HMI. RS-485 communication was used to achieve remote control to drive unit, which improved the system integration and reliability. The system guarantees the bag transporting location and liquid filling accurately. It realizes real time detection of length and speed. It can be stably and reliably used in field