This paper discusses the analysis and optimization of a novel optomechanical structure based on a Wood's type anomaly, in which tiny changes in the spacing of the nanostructured grating elements lead to a dramatic increase or decrease of the optical reflection amplitude. With this special feature, this structure is an ideal sensor component to observe very small amount of relative motion. This device is very sensitive to light source wavelength, the period and the width of the grating. Here, we analyze the performance of the structure with different parameters and incident light of different wavelengths through 3-D Finite Difference Time Domain method (FDTD). Simulation gives out the respective influence of those parameters and the optimized structure designs for different wavelengths which are most possible to fabricate with current surface micromachining processing similar to that used for the fabrication of polysilicon MEMS. The calculated data enables us to apply the structure into fields required for different sensitivities and dynamic ranges with different grating designs and thus broadens the further usage of such novel structure.