The vibration of power transformer on oil tank, which mainly comes from the vibration of core and winding, contains rich information to demonstrate transformer mechanical condition. This paper using vibration characteristics like the vibration eigenvalues in spectrum, the proportion of frequency, the maximum amplitude of vibration spectrum and the complexity of vibration spectrum to research transformer tank vibration under certain faults. In the lab, faults like core looseness, winding looseness and displacement in radial direction of winding were set in a 10/0.4 kV three phases power transformer. The conclusion shows that the complexity of vibration spectrum decreases at all above there faults, amplitude of fundamental frequency increases at core and winding loose and decreases at displacement in radial direction of winding fault. The conclusion of this paper may make contributions to the condition monitoring technology of transformer.