The invention discloses a rotating shaft axial displacement detection method and device and a magnetic suspension bearing system. Steps are arranged on a rotating shaft to be detected. The method comprises the steps that electric signals outputted by radial probes are detected, the radial probes are arranged in the radial direction of the rotating shaft to be detected and arranged to be opposite to the steps, and the radial probes are used for sensing effective detection area of the steps and outputting the electric signals corresponding to the effective detection area; and axial displacement of the rotating shaft to be detected is determined according to the electric signals. With application of the rotating shaft axial displacement detection method and device and the magnetic suspension bearing system, the problem of low accuracy of the detection method of detecting displacement of an axial detection surface through axial probes to act as axial displacement of the rotating shaft in the prior art can be solved.