In this paper,the first readout circuit of small pixel infrared detector based on SMIC 0.18 μm 3.3 V process design is introduced.The readout circuit has a spacing of 10μm and a size of 1024×1024.The design of pixel input stage and column stage and output stage operational amplifier is introduced in detail.In order to improve the linear swing voltage,a low threshold transistor(nmvt 33) is selected.The simulation result shows that the noise performance of nmvt 33 is better than that of ordinary transistor(n 33).In layout design,isolation measures are adopted for key signal lines and sensitive points.Crosstalk between pixels is simulated and analyzed,and signal crosstalk is effectively controlled.The circuit has been tested and used with normal functions.Its maximum charge handling capacity is 4.3 Me-,dynamic range is more than 65 dB,readout rate is 10 MHz,and performance index meets the design requirements.