This paper presents the readout circuit applied in Infrared Detector signal processing circuit.The basic readout circuit unit is designed with an improved current mirroring integration（CMI）architecture,namely using the wide-output-swing and self-biased current mirror to optimize the traditional CMI circuit,This structure uses a high-swing self-bias P-type cascode current mirroring and an N-type current mirroring forming the feedback structure which greatly enhances the stability of the current mirror,the power dissipation of the basic readout circuit unit is reduced by 3.3μW.A detailed analysis of the improved CMI circuit with its architecture,working principle as well as design process is carried out in this paper.The total circuit is simulated and implemented using Chartered 0.35μm integrated technology.The simulation results indicate that the CMI circuit successfully completes the current integrating function with the current from 30pA to 4.5nA and meets the 9-bit accuracy.