Abstract: In order to avoid direction error of rotating shaft during the running of belt conveyor due to equipment failure or operational errors, a direction detector was designed. On the basis of the relative motion of gear pair and one-way clutch, the detection of the rotating direction of a shaft was transformed into the detection of signal from proximity switch, and determined by a PLC controller. The device was tested on a two-way belt conveyor, the results showed that this device could monitor the running state of belt conveyor with the accuracy of 100%, correct the running status of processing line timely. The maintenance response time was shortened by 5 min. This device provides a technical support for promoting the process control level of tobacco primary processing.