Abstract: In view of problem that loading accuracy and loading quality could not be ensured because of serious overloading existed in loading system of Coal Preparation Plant of Nantun Coal Mine, an automatic unloading system was designed, design of hardware and software of the system was introduced. The automatic unloading system is added a coal unloading unit. When train passed through metering scale, the system can get metering information of train by communication with original automatic loading coal system. If the train is overloaded, the coal unloading unit would go down to unload coal. A metering system is installed on coal back belt. The system realizes automation of overloading and unloading of train.