Abstract Rain rate is measured by a rain gauge, radar reflectivity and special differential phase shift traditionally. In this paper, a new way of estimating rain rate using rain-induced depolarization characteristics of Global Navigation Satellite System (GNSS) signals was studied. Using the cross-polarization discrimination (XPD) which is defined to describe the effect of depolarization, the relationship between XPD and rain rate (R) was presented based on the oblate spheroid raindrop model and Marshall–Palmer raindrop size distribution model. The sensibility of XPD with rain rate, rain path length and elevation of GNSS satellites was simulated systematically. Simulation results show that XPD is sensitive to rain rate and the XPD–R relation can be employed to evaluate the rain rate. The novel method for real-time, continuous, regional detection of rain rate explored in this paper will find applications in the nowcasting automated detection of global heavy rain reconnaissance.