A method of determining bearing preload by vibration measurement including mounting the bearing on a vibration tester, the outer ring clamped preventing rotation, mounting a sensor proximate the outer ring to measure vibration, the bearing inner ring rotated to excavate eigen-frequencies, the measured vibration data transmitted from the sensor to a computer workstation, the computer workstation performs a numerical FFT transforming data to Frequency Domain, spectral data from the FFT analyzed with the computer workstation, a peak detection algorithm determines the peaks that are the various modes of the outer ring, the modes are sorted and main modes identified, numerical relationship is obtained for each mode between the resonance and preload, the mode relationships are compared to one or more references, a match between the numerical relationships for each mode and the ideally referenced graph modes indicates a correct preload is determined. Also, a system for carrying out the method.