The invention relates to a new method for the fault diagnosis of a rotating machine based on precession energy difference density spectrum analysis, and belongs to the technical field of mechanical fault diagnosis. Aiming at defects that a method for describing fault features through employing a filter shaft center orbit is low in resolution and is not visual in representation, the method constructs a new fault feature parameter-precession energy difference density, wherein the magnitude of the new fault feature parameter-precession energy difference density is in direct proportion to the square of an amplitude spectrum. The method achieves higher precision and resolution, and can visually display the forwarding and reverse precession energy features of a rotor. Moreover, the method further obtains a precession energy difference density spectrum, and can carry out the diagnosis of a fault of a rotating machine more accurately through combing with the filter shaft center orbit. The method comprises the following steps: 1, carrying out the signal collection and processing, and obtaining forwarding and reverse precession parameters; 2, constructing a fault feature parameter model-precession energy difference density; 3, drawing the precession energy difference density spectrum, and carrying out the fault diagnosis and analysis through combing with the filter shaft center orbit.