The joint influence of multipath propagation and rain attenuation effects and also the land and rain clutter on the millimeter wave radar operation, in particular, on the maximum detection range and target detectability is considered. The parameters of millimeter wave radar are compared with parameters of analogous radar of X-band and the comparison is carried out for two cases: with frequency change an antenna aperture is constant (1) and with frequency change an antenna gain is constant, i.e. the proportional change of antenna aperture takes the place (2). The results of this analysis are presented for different types of terrain (quasi-smooth, rough, rough with vegetation, etc.) and rains with intensity from 2 to 10 mm/h. It is shown that for constant antenna aperture and joint effects of multipath propagation and rain attenuation the all-weather millimeter wave radar is more effective than analogous X-band radar at ranges less than 2 - 4 km.