Nowadays, traditional infrared detectors such as MCT infrared photo detectors performance nearly reached their detect theory limits. As lead to an increased interest in detectors such as QWIPs, T2SL, QCD and so on. Due to the low cost, high integration level and high performance, QWIPs is a mainstream infrared photo detector in the areas of military, medicine industries. The problem blocked the QWIPs industry development is the low quantum efficiency because of the polarization dependence of the incident light. As decided by the absorption mechanism, the QWIPs cannot absorb the normal incident infrared light. Various methods is developed to couple the normal incident light to the QWIPs. The introduction of metal gratings proved to be efficient to improve the absorption of the normal incident light which can introduce a SPPs coupling on the interface of the gratings and the QWIPs. But in the method used before usually are transmission gratings on the surface of the QWIPs devices. A kind of backscattering metal grating patterns is designed and simulated in our work to get a higher performance. It is nearly 4 times of the coupling efficiency than the transmission gratings in simulation. We also discuss some grating parameters such as grating thickness and cycle duties for their effects on the coupling efficiency and optimize these parameters to reach a highest performance. The simulation results show a new promising structure use in the QWIPs especially in the dual-band QWIPs to enhance the absorption of the long wavelength infrared light.