This study proposes an optimization method for detecting the low-frequency vibration of a cantilever beam using the 3 dB point of the resonant peak of an excessively tilted fiber grating (Ex-TFG). First, the axial and bending strain characteristics of Ex-TFG are theoretically analyzed and experimentally verified. The spectral response characteristics of the Ex-TFG vibration sensor modulated by light intensity are also theoretically analyzed. The 3 dB point of the Ex-TFG resonance peak is proposed to detect the vibration signal, and subsequently, a corresponding experimental research is conducted. The results are as follows. First, the resonance wavelength of Ex-TFG is blue shifted owing to both axial and bending strains. The axial strain sensitivities are -2.8 and -1.8 pm/με for the TE and TM modes, respectively, whereas the transmission intensity remains unchanged. Bending strain sensitivities based on the light intensity modulation in the curvature range of 0-0.4 m -1 are 2.6 dB/m -1 and 1.2 dB/m -1, respectively. Bending strain sensitivities based on wavelength shift are -3.34 nm/m -1 and -2.53 nm/m -1, respectively. Second, during vibration detection, the vibration acceleration sensitivities of the resonance peaks of Ex-TFG at the 3 dB points are 113.54 and 100.93 mV/g for the TE and TM modes, respectively, which are over two times higher than those (100% point) of the resonance peaks. The signal-to-noise ratios (SNRs) of the TE and TM modes at the 3 dB point are also higher (approximately 10 dB) than those (100% point) of the resonance peaks. In addition, the SNR increases with the increasing cantilever beam thickness. Third, under the same condition, the TE mode exhibits higher vibration response sensitivity than the TM mode; however, the output of the TM mode has better stability than the TE mode.