Abstract: A kind of infrared focal plane CMOS (complementary metal oxide semiconductor) read out integrated circuit (ROIC) for small pixel applications was developed. This ROIC design includes ITR(integration then reading) and IWR(integration while reading)functions, two gains in ITR mode, charge capacities are 4.3 Me^- and 1.6 Me^-. Other functions include anti-blooming, series port control function and full chip current injection test function. This ROIC was fabricated in 0.18μm process, power supply voltage 3.3 V, test result show good performance of the ROIC, full frame rate is 100 Hz, noise of readout circuit is 0.2 mV. This paper introduces the basic structure of the readout circuit design, and analyzes the design of anti-interference ability of the circuit under the condition of small integral capacitance; During the test, tailing phenomenon is found, the causes of the tailing phenomenon is analyzed and In order to solve the tailing phenomenon, the Anti-blooming voltage generation circuit is designed, and the test results of the whole circuit are given at the end of the paper.