Focusing on the simultaneous integration mode of N+PPN structured MW/ LW 2-color IRFPA, this paper presents a novel readout input circuit, which is based on the GMI input structure. By using the current mirror, the independent band (LW) signal can be duplicated. The two duplicated signals are used for integration of LW signal and subtraction from the mixed signals, and MW signal is separated. The LW signal and MW signal can be integrated simultaneously. This paper gives a detailed description of the structure and operation principle of the input circuit. The results of simulation and verification indicate that this circuit is suitable for the 2color IRFPA with signal current>10nA (MW/LW, MW1/MW2,LW1/LW2 devices) and it has high accuracy(error<2%) and well performances.