Satellite signals across the space-earth link are always seriously affected by rain, inducing attenuation and depolarization. In this paper, two methods of estimating the rain rate are investigated based on the space-earth link signals in a frequency range of 1–10 GHz. Firstly, the effects of rain rate (R) on attenuation (A) and cross-polarization discrimination (XPD) are studied, according to the complex interaction between signals and raindrops. Then, two relevant models A-R and XPD-R are established, which are the key techniques to estimate the rain rate. The feasibilities of the above models are analyzed. In addition, their applicabilities at various frequencies, polarization and satellite elevations are also investigated systematically. The results show that for the space-earth link signal with horizontal or circular polarization and higher frequency, the A-R relation can be used to estimate the heavy rain; for signals with different frequencies and polarizations, XPD-R is suited to estimate various rain rates, especially in a frequency range of 1–50 mm·h-1; A-R and XPD-R are both applicable at different elevations. Moreover, the XPD-R relation is consistent with the prediction model of XPD proposed by ITU at 4–10 GHz. The results obtained in this work will play an important role in the future verification experiment, the nowcasting automatic detection of rain rate and global rain observations.