Abstract: Quantum well infrared photodetector(QWIP) has been comprehensively and thoroughly studied for more than 20 years. The research and preparation of many kinds of QWIP devices including QWIP focal plane array(FPA) become quite mature. However, restrained by the whole domestic industrial development level, the research and fabrication of QWIP FPAs is still on relatively low level in home. We fabricated 320256 n-type QWIP FPA based on GaAs/ AlxGa1-xAs. The cutoff wavelength was 9.9 m, mesa center distance was 25 m and active sensitive area was 22 m22 m. After GaAs-substrate thinning, the QWIP FPA was flip-chip bonded to a silicon based CMOS read out integrated circuit(ROIC) by indium bump. Infrared images of targets at room temperature background were taken at 65 K operating temperature. The scale of the FPA and the quality of images were improved comparing with the former interior result. The mean peak detectivity of the FPA reached 1.51010 cmHz1/2/W.