Detector structures,work modes and signal input circuits for dual band infrared focal plane array are re-seached. Two signal input stage of readout circuits for our dual band IRFPA are presentsed, and simulation on the cir-cuits is carried out. The input stages of both simultaneous SW /MW dual-band FPAs and sequence SW /MW dual-band FPAs are direct injection circuits. Photocurrents resulting from the detection of two spectral band are integrated in each capacitor, and the signals then are put to latter processing circuits.