As the main remote sensing means for cloud detection, millimeter wave cloud measurement radars can provide timely, accurate and reliable information for the inversion of macroscopic and microscopic parameters of cloud. The study of the calibration technology for millimeter wave cloud radars is not only helpful to the full use of their observation data, but also is helpful to the improvement of observation quality. Although the internal calibration systems for millimeter wave cloud radars can automatically detect the main operation parameters and revise the detected results so as to keep the stability and authenticity of the detected results, they do not take the antenna characteristics and the interaction among different components into consideration. Therefore, it is particularly urgent to study the external calibration technology for millimeter wave cloud radars. On the basis of the external calibration experiments of airborne millimeter wave cloud radars at home and abroad, the external calibration technologies are presented and analyzed and the process of external calibration is determined. This provides the reference for the initial airborne external calibration experiment in our country in the future.