Abstract: The existence of radio duct within the troposphere could make electromagnetic waves achieve overthehorizon propagation， which is important for the performance of radar and communication system. In order to get the distribution of basic transmission loss so as to achieve maximum power receiving in overthehorizon position, a new researching method of radio duct transmission character using nonradardetection is proposed. By matching the simulation value and target value of basic transmission loss at the inversion place, it is to inverse the character of radio duct, and then get the 2D distribution of basic transmission propagation loss. The simulation results show that the method is feasible. Preliminary discuss is taken on the inverse position choice.