A thin-cladding Excessively Tilted Fiber Gratings （ExTFG） cantilever beam vibration sensor is reported in this paper. Using the ExTFG written in the standard single-mode fiber， the effects of the decrease of the fiber cladding radius on the dispersion factor of the waveguide， the effective refractive index of the cladding mode， the axial strain sensitivity factor， the axial strain sensitivity and the mode order are theoretically analyzed， and the corresponding numerical simulations are performed， which provide the theoretical foundation for the enhancement method of vibration measuring sensitivity. And then， hydrofluoric acid is used to etch the fiber cladding to fabricate ExTFGs with different diameters and the related vibration sensing experiments are conducted. The results show that in the vibration frequency range of 40~200 Hz， with the decrease of cladding diameter， the acceleration sensitivity of ExTFG vibration sensor in C band of the same order and different order TE/TM mode increases gradually， and there is a good linear relationship between them. The maximum acceleration sensitivity of the TE and TM mode with the same-order cladding mode is 100.46 mV/g and 88.68 mV/g， respectively， which is increased by 1.36 times and 1.53 times， respectively， as compared with the standard diameter one. And the maximum acceleration sensitivity of those with different-order cladding modes can reach 159.35 mV/g and 133.37 mV/g， respectively， which is increased by 2.15 times and 2.31 times.