An accuratenoise model was established for the infrared imageinformation acquiring system.In the simulation and test, noise characteristics were analyzed. The results of the three are almost same, about 0.11mV. Both theory and experiment proved that signal conditioning circuit based on instrumentation amplifier can be used for low-noise infrared detectors. The noise level was analyzed together with the spectral characteristics of the circuit noise. The results show that the main components of the noise are 1/f noise and white noise. Both of the two meet the Gaussian distribution.