Abstract: The spatial noise on staring array thermal imager restricts its capability in detecting, distinguishing and tracking the long distance targets. To solve the problem in measuring the thermal imager spatial noise, its measuring theory was analyzed and the mathematical model for measuring the spatial noise based on signal transfer function (SiTF) was presented. After removing the temporal noise equivalent temperature difference (NETD) from the noise of a certain group or district or the whole pixels in thermal imager, the spatial NETD model was calculated through analyzing statistically the noise of those pixels. In measuring the SiTF and spatial NETD of cooled MCT320256 thermal imager, when the temperature of the background blackbody is 5 ℃, the SiTF of central district in field of view(FOV) is 27.29 mV/℃, and the spatial NETD is 0.128 ℃. When the temperature of the background blackbody is 20 ℃, the SiTF of central district in FOV is 29.03 mV/℃, and the spatial NETD is 0.121 ℃。The measuring results show that the measuring method can evaluate the influence of spatial noise on the performance of thermal imager.