To enhance quantum efficiency of infrared detectors made of PtSi Schottky barrier, the flat interface of PtSi/p-silicon metal semiconductor was modified to a grating structure. The incident radiation can be coupled with the surface plasma waves within this structure, thus to improve the optical coupling efficiency of the PtSi infrared detector. Based on rigorous coupled-wave analysis method, parameters of the grating structure were optimized and electric field distributions at resonant wavelength were simulated. The quantitative relationship between the optical coupling efficiency and quantum efficiency of PtSi Schottky barrier infrared detector was discussed. Comparing with the flat structure, the average quantum efficiency is evenly increased twice in 3~5 μm wavelength range, and approximately 2.94 and 2.5 times at 3 μm and 3.4 μm, respectively.