Objective To develop a fault detection system to settle the problem of high failure rate in packaging. Methods Sensing signals of some key parts were collected by PLC. The key parts were conveyor belts, motors, flip folding mechanism, folding shovel, sealed bags shovel, bagging shovel and so on. Then applying the fault tree principle, real-time diagnosis was made and displayed for the collected signals using the upper computer system designed by Visual Basic. Results Practice has proved that this fault detection system is highly reliable and effective. It could improve production efficiency through improving the troubleshooting capabilities of the machine. Conclusion The user interface of the system is simple, easy to operate, reliable and with high degree of automation. It can effectively reduce troubleshooting time and has important significance for the routine maintenance of the packaging machine.