For longarray FPA device, simple cold shield couldn′t effetely restrain background illumination. In this paper, the question has solved by depositing microaperture cold shield at the back of HgCdTe photovoltage detector. The test results show that microaperture cold shield can reduce background illumination after deposited on the detector and also can reduce the cross talk. So microaperture cold shield can effective restrain the background flux and hold the natural response area of pixel when detector is working. This process can improve the capability of infrared FPA detector.