Abstract: The low frequency noises of two types of HgCdTe medium wave photoconductive infrareddetectors were measured and analyzed. The noise of detectors with contact overlap structure is larger than that of conventional ones. An edge contacts asymmetrical metal insulator-semiconductor modelis put forward to explain the noise character. The larger noise of overlap structure is mainly causedby the depletion layer, which will appear under overlap electrodes when the detectors are biased.