Digital technique is one of the representative of the third generation Infrared Focal Plane Array(IRFPA). By implementing the focal plane array digital,greatly expanded the limit of the detection sensitivity,improve the response speed of the system,and combat effectiveness of the system,it can also make the system have higher reliability and performance than the second generation of IRFPA. Analog to digital converter(ADC) is an important part of digital FPA,especially the pixel-level ADC,It has an irreplaceable advantage because it can extend the dynamic range,improve the anti-jamming ability and subsequent transmission path signal processing flexibility. This paper introduces the characteristic of several typical pixel-level ADC structures and their effects on the performance of IRFPA,and the latest development of pixel-level digitization technique.