This study focuses on the application of a modified digital elevation model (DEM) method that not only considers geometrical power losses but also addresses effects such as power losses caused by ground-clutter filtering and the radar system’s calibration errors. X-band dual-polarization radars operated by the Ministry of Land, Infrastructure, Transport and Tourism of Japan are located near mountainous terrain in the southern part of the Kanto region in Japan, at Fujinomiya and Shizukita. Both radars suffer from problems caused by partial beam shielding at various low-elevation angles, which lead to underestimation of the amount of rainfall. After correcting for reflectivity attenuation, a modified DEM method was applied to correct for bias reflectivity in the presence of beam-shielding problems. Validation of the corrected reflectivity based on comparison tests shows that the modified DEM method significantly improved the bias reflectivity caused by partial beam blocking.