Abstract: The relationship between integration time and the output signal of IRFPA imaging system was theoretically analyzed with the CTIA readout circuit. The results indicate the variation of the output voltage is proportional to the integration time when the parameters of the circuit are fixed. The relationship between integration time and noise, and the relationship between integration time and specific detectivity were analyzed with the electrons method. The non-linear relationship of the integration time, noise and specific detectivity was derived. The influence of the integration time variation on the non-uniformity was analyzed. The changing trend and the influence result were proved by the experiments. It shows that the integration time is very important to the design of IRFPA imaging systems.