In order to adapt to the development direction of high density and minization of the third generation infrared focal plane, a large array small pixel and low power consumption of 640×512-5μm InGaAs shortwave infrared focal plane readout circuit was designed in this paper. The performance of the simple structure of 3T pixel unit was studied, and its influence on the chip dark current and focal plane noise was analyzed to realize the rolling curtain exposure operation mode, the dynamic operation of column level buffer and the four-channel output function. Programmable gain amplifier was used to achieve gain adjustment and noise suppression. Based on the standard CMOS technology of 0.18μm 3.3V, the performance analysis of the small pixel unit and the four-channel output of the array window and the linearity simulation were carried out at the input clock frequency of 5MHz. The results show that the bias change of the input stage of CTIA is about 30mV, the working frame frequency is 54Hz, the output swing is 1.7V, the maximum power consumption is less than 150mW, and the linearity is 99.987%.