The long-wave infrared detectors present the characteristics of large dark current, high background, large charge capacity readout circuit was need to design. A designing scheme of a high readout efficiency and large charge capacity readout circuit for 320×256 LW infrared focal plane arrays(IRFPAs) in the finite cell area of FPAs was proposed by adopting the circuit structure of time-shared the integrating capacitor. The input stage circuit used the capacitor feedback transimpedance amplifier (CTIA) preamplifier structure, which has a high injection efficiency, low noise and good linearity. The simulation and the simulation after completing the layout were carried out based on CSMC 0.35 μm standard CMOS process model, the output swings of circuit were larger than 2 V and the nonlinearity is less than 1%, the frame rate is 100 f/s, after adopting the circuit structure of the time-shared integrating capacitor, the effective charge capacity reached 57.5 Me-/pixel.