A new type of structure which is composed of a Gaussian profile-shaped metallic nanograting, was put forth from the nanofabrication point of view. Dependence of the structural parameters on the sensitivity was analyzed by means of a multiple multipole program (MMP) method. One of the important applications of the nanograting is in biosensing: immunoassay. Our numerical simulation results showed that the sensitivity to refractive index of 490 nm/RIU and the reflection spectra at site of full-width at halfmaximum (FWHM) ~9 nm can be obtained through the optimized structure. The figure of merit (FOM) of the sensor can exceed 55. The resonant wavelength increases linearly with increasing of the refractive index of bio-samples. These reflection properties make the nanograting more suitable to be used in the localized surface plasma resonance (LSPR)-based biosensors for immunoassay.