In this study, we emphasized on effects of grating slant angle of tilted dielectric gratings (TG) on surface plasmon resonance (SPR). The momentum conservation for an optical wave exciting an SPR via TG is different from unslant gratings. The coupling condition induces the period along the grating surface (in the direction x) be decided not only by grating period but also by slant angle. The results calculated by rigorous coupled-wave analysis theory (RCWA) indicate that the resonant wavelength and the refractive index sensitivity are strongly dependent on the period in the direction x (noted Λx). And the refractive index sensitivity increases with the rise of the period Λx. The SPR sensor through TG offers high sensitivity about 800nm per refractive index unit and narrow full-width at half maximum (FWHM) about 5nm when monitoring biochemical liquid solutions.