Aiming at the application requirements of brightness temperature calibration of the hot calibration target of spaceborne microwave radiometer， and based on the temperature gradient characteristics of the absorbing coating of the calibration target and the mechanism of brightness temperature deviation， combined with practical temperature measurement and experimental methodology， a brightness temperature metrological calibration technology solution applicable for in-orbit use is studied. Given the current background of high emissivity design and determination technology of the calibration target being basically perfected， this work focuses on summarizing the methods for determining the temperature gradient characteristics of the calibration target coating. The goal is to construct an in-orbit available brightness temperature calibration method that uses multiple parameters， such as the measurable temperature values of the metal inner core of the calibration target and that near the radiation aperture of the calibration target. Based on feasible electromagnetic simulation technology， thermal simulation technology， platinum resistance and infrared temperature measurement techniques， the paper preliminarily summarizes the implementation path of the brightness temperature calibration technology system for space-borne calibration targets. This involves first constructing a basic brightness temperature calibration model considering uniform background brightness temperature and improving the mapping relationship from the inner core temperature of the calibration target and the equivalent background brightness temperature to the longitudinal temperature gradient of the coating. Subsequently， an application model for brightness temperature calibration considering the installation environment is constructed， improving the mapping relationship from the temperature measurements of the inner core and that of the radiation aperture area of calibration target to the overall brightness temperature deviation. Finally， the validation and application of the brightness temperature calibration model are discussed. The research on brightness temperature calibration of space-borne calibration source is an important technical basis and reference for further improving the accuracy of brightness temperature of calibration target and even developing space microwave radiation measurement standards.