Millimeter-wave (MMW) radiation characteristics of solid targets are very complex, this paper started with the research on modeling and simulation of the metal ball. Due to the property of millimeter-wave resembling light, the ray tracing theory was used to analyze the two-ray propagation of direct reflection and ground secondary reflection of the metal ball surface. The radiation temperature calculation model was established and the MATLAB simulation platform of millimeter-wave radiation characteristics of the metal ball was achieved based on the geometric model of triangle surface element division of the metal ball and the space geometry relation of relative motions between detector and target. The validity of the modeling method is verified through the antenna temperature curves of metal ball and round metal plate under given simulation conditions, and the results show that the metal ball can be equivalent to a nonmetal round plane target with 1.3 times linear size through comparative analysis of the signal waveform characteristics, which provides more accurate and effective data and theoretical support for target recognition and localization in millimeter-wave passive detection.