For the most commonly used GaAs/ AlGaAs quantum well infrared detector (QWIP), normal incident absorption is not possible due to the transition rules. QWIP requires gratings to achieve high absorption quantum efficiency and the shape of the grating affects the peak response wavelength. In order to reduce the impact of other processes on the spectrum, we manufactured 320 × 256 n-type QWIP focal plane array (FPA) was fabricated based on GaAs/AlxGa1−xAs. 160 × 256 were concave gratings and 160 × 256 were convex gratings. Three-dimensional(3D) model was first exploited and the response spectrum of two gratings were calculated by the finite difference time domain (FDTD). The test result indicated that concave grating response wavelength was 11.2μm, convex grating response wavelength was 10.3μm. The operable pixel factor of the QWIP FPA was 99.494%, the average responsivity was 17.95 mV/K. In addition, we obtained infrared images based on QWIP FPA.