In order to test the performance of millimeter wave detector in the actual working status and analysis of it on the target characteristics of the output signal, this paper studies the working principle of millimeter wave radiometer and output signal expression.The characteristics of the radiometer output signal are studied by simulating experiment in the field and obtaining the data of semiphysical simulation. Without considering atmospheric loss and the effect of antenna sidelobe, 3 mm is deduced and 8 mm radiometer antenna temperature contrast in detecting cement road surface and the maximum detection range, and through the analysis of the experimental data are compared both performance, provide the basis for selection of radiometer.