The infrared detector module is the key device of target detection and imaging system. Its spatial resolution directly affects imaging quality of detection system. When evaluating the spatial resolution of detector modules, researchers usually adopt modulation transfer function (MTF), which is influenced by the different structures of the detector modules. The basic principle and configuration of infrared micron-spot test system with an optical dispersion diameter of 30 μm was introduced. MTF of detectors with different structures was measured by scanning slit technique. The results show that the profile of overlap electric region is photosensitive. This is the main factor to widen the line spread functions(LSF), cause the secondary peak, and so on. The MTF is thus deteriorated. Meanwhile, the different distance of chip and filter with 0.17 mm and 0.30 mm influences slightly the optical crosstalk of the detector module. These results are used for optimizing design of infrared detector modules for stray light control.