Method for interpretation of radiometrically measured microwave signal by numerical simulation of radiometric signal generation inside multi-layered breast tissues has been developed using FDTD method. A radiometric system for exploration of breast tumors based on a Dicke radiometer with two body-contacting waveguide antennas has been designed. Special software for presentation of data about configuration of the breast under investigation, the measurement point position on it, level and co-ordinate of the radiometric signal provides possibility for the interpretation of radiometric signal for tumor detection by comparison of calculated and measured signal field distributions. The results of calculations showed that Dicke radiometer having temperature resolution better than 1 K can be used with two dielectric-filled body-contacting waveguide antennas for exploration of tumors which are at least 6 mm in diameter. The preliminary clinical measurements show, that the radiometric system is working better in the case of small sizes of anomalies.