In this paper, the relationship between vibration and fatigue life of metal has been investigated. To perform the research, finite element method is used to design two types of steel specimen before the experiment under bending load is conducted on an electro dynamic shaker. In the experiment, the tested frequenciesare around the first natural frequency of the specimens and they are carried out at the frequency ratios r = f/fn (f = excitation frequency, fn = natural frequency) = 0.9010, 0.9792, 1.0000, 1.0200, 1.0900. The frequency ratio is used instead of frequency in order to get rid of the error occurs because the first natural frequencies of the specimens are not exactly the same. The amplitude of the vibration is conducted at the constant acceleration of 10g (g = 9.81m/s2). The results from both finite element method and experiment show that at the constant acceleration with respect to the variation of frequency ratio, the fatigue life increases as the frequency ratio increases.