Abstract: According to the special application environment of granary,from the radar detection quality factor and the scattering cross-sectional characteristic of granary’s bottom and combined with attenuation factors of grain medium,  the calculation formula of radar’s maximum investigation depth was deduced and  a simulated analysis on factors which influence the investigation depth was made. Finally,the appropriate radar system and radiation frequency in accordance with the calculation method in this paper were selected to conduct the experiment of granary detection and detect the granary’s depth accurately