：Long-wavelength IRFPAs,which have large dark currents,usually work under high backgrounds.By contrast,the photo current proportion is much smaller than the back-ground current.Compared with short and medium wavelength,the integration capacitor is more easily saturated.But we can not increase the capacitor too big because of the area of the chip,and all of these lead to a poor SNR.To the question of the LWIR FPAs,This paper will discuss and analyze the various techniques and approaches for design of ROIC,and achieve it with high performance.