Abstract: Acoustic Emission(AE) monitoring method was used to diagnose the contact friction fault of a plain bearing under dead-load.On a controllable test rig,liquid lubrication to dry friction was controlled by cutting off lubricating oil for various durations.The experiment parameters were normalized so as to realize convenient and simplified diagnosis.The applicability of the resulting non-dimensional diagnosis rule to the diagnosis of the contact fault of the bearing was investigated.As compared with vibration monitoring method,AE signals have a more wide range of frequency response and large information amount,which can effectively reflect the faults of a plain bearing.AE signals is more stable and character of fault is clear and can be easily detected in comparison with vibration signals.