Abstract: A plain bearing with dead-load was performed to simulate the fault occurrence and development of the axle journal and bearing running at different lubricating conditions. The transition of the bearing operation states from oil-lubricated running to dry-running was realized by cutting off the lubricating oil for various durations. The corresponding vibration signals were monitored and normalized so as to realize convenient and simplified diagnosis of the contact frictional fault of the plain bearing. Thus the characteristic parameters of the bearing with respect to the fault states were divided by the ones with respect to the normal state under the same operating conditions so as to establish the non-dimensional diagnosis principle based on the non-dimensional characteristics parameters. The applicability of the resulting non-dimensional diagnosis principle to the diagnosis of the contact fault of the bearing was investigated. As the results, it was unnecessary to construct the standard model for pattern recognition, making use of the established non-dimensional diagnosis principle insensitive to different operating modes but sensitive to the fault modes. Therefore, the established non-dimensional diagnosis principle was applicable to the trouble diagnosis of plain bearing in variant operating modes with significantly lowered diagnosis cost.