Short-period fiber Bragg gratings with gratings planes tilted at a weak angle corresponding to the fiber axis show core mode, as well as a large number of cladding-mode resonances in transmission. Tilted fiber Bragg grating (TFBG) with different cladding diameters is achieved after the cladding of the tilted fiber Bragg grating is etched by hydrofluoric, and then the sensitivity of refractive index is investigated. While the surrounding refractive index changes from 1.333 to 1.4532, the high-order cladding modes are more sensitive than the low-order ones for the same diameter. The sensitivity of the cladding modes is enhanced with the decrease of cladding diameter, and it is custom-built more sensitive to surrounding refractive index. Therefore, this way not only can solve temperature-crossing sensitivity problem, but also can satisfy the custom-built sensitivity in the real-time monitoring systems by etching the clad of TFBG in different degrees. It can be applied to biochemical environmental sensing and concentration measurement of chemical solutions.