For the fact that energy loss will change when there is some faults with the gear,a new fault diagnosis method of gear based on energy loss was put forward and corresponding fault rules were set up.The gear tribological system and the energy loss theory were researched a test bed monitoring the energy loss of gear was designed to obtain the information of energy loss,and choosing the input power as the energy loss information of the gear,the extraction method of neural network and fuzzy theory were adopted to modify the rules and build the fuzzy fault rules of gears energy loss information.The result shows that fault diagnosis rules of gear based on energy loss are effective and accurate,which lays the foundation for realizing the fault diagnosis based on energy loss.