According to the short integration time characteristics of long wave infra-red focal plane array, the principle and application of oversample-superpositon technique were discussed. The effect of oversample-superpositon on the MTF of system was analyzed on the basis of the chareaeteristics of LWIR FPA. The corresponding oversample-superpositon MTFs at different sampling and superpositon time were given. As the superposion time deereases, the detector MTF is reducing while system scanning MTF ix rising when the sampling time is fixed.