An improved algorithm for calculating the temperature and depth of a cancerous tumor in the depth of the human body by the method of multi-frequency multi-channel radiothermography is considered. An improved model is presented to describe the processes of receiving the human body's own radiothermal field by a multi-channel multi-frequency radiothermograph. The possibility of simultaneous calculation of temperature, the depth of the location under the skin and the size of the tumor is analyzed. The conditions for determining these values depending on the parameters of the tumor and the radiothermograph are investigated. The maximum possible depth of tumor detection is determined depending on the parameters of the radiothermograph and the thermal contrast in the source. The necessity of increasing the number of frequency ranges of the radiothermograph is justified. The results of calculating brightness temperatures at different depths of occurrence and tumor temperature are presented in the framework of an improved model. © 2022 Russian Academy of Natural Science. All rights reserved.