Abstract: Because of the random characteristics of microwave signals, the inversed images of synthetic aperture radiometer have random characteristics. The statistical distribution model based on inversed images is built. The method for calculating the detection probabilities of inversed images is presented. The formula for calculating the maximum distance of detecting target by synthetic aperture radiometer is deduced. At last, the performance of detecting stealthy targets by synthetic aperture radiometer is analyzed using 100 unit Tshape antenna configuration as an example and the method is verified by computer simulation. The research in this paper is much of help in the application of stealthy targets detection using synthetic aperture radiometer.