With the recent emphasis on understanding the role of clouds in the global radiation budget, cloud detection becomes more and more important. Although there are optical remote sensing techniques (e.g., satellite lidar, ceilometer, etc.) to measure cloud properties, optical signals cannot penetrate into thick cloud to observe the cloud′s horizontal and vertical dimensions and its internal structure. The scope of radar meteorology has expanded to include measurements of cloud properties and structure for radar′s wavelength is close to cloud′s diameter. Millimeter-wavelength radar is recognized as having the potential to provide a more sensitive probe of cloud particles ranging from a few micrometers in diameter to precipitation drops. Since the backscatter cross section of tiny drops (i.e., several tens of micrometers in diameter) increases in proportion to λ^-4, where  λ is the radar wavelength, cloud drops are more easily detected by radars of millimeter rather than centimeter wavelengths. On the other hand, attenuation of millimeter waves is much stronger, and the λ^-4 advantage gained using millimeter waves is offset by the strong attenuation these waves experience. The 10-cm-wavelength radar, used principally for storm warnings, cannot detect weak and no precipitation clouds well, compared with the mm radars. Compared to normal weather radar, millimeter wavelength radar has following superiorities in observing clouds: ①strong capability in detecting small particles like cloud, fog and dust; ②better resolution and precision of Doppler velocity; ③high special resolution result from its narrow beamwidth. In this paper, the status about cloud radar in and abroad about radars′ technology and application on clouds′ micro and macrophysics research, airports safe flight are introduced. Also present is a prospect on millimeter-wavelength radar.