GNSS-R technology uses the GNSS reflected signals for remote sensing of the Earth. It uses delay Doppler mapping equipment (DDMI) carried on different platforms to receive the reflected signals from the Earth’s surface and the receiver’s local replica code, and measured the scattering power of the Earth’s surface as well as inverted the geophysical parameters of interest. Recently, there have also been experimental studies that directly coherently processing the reflected signals and direct signals to augment the radar signals with improving ranging accuracy and spatial resolution. Because GNSS-R uses the working mode of bistatic radar, it directly uses the GNSS signals that are ubiquitous in space. The deployment of the GNSS-R observation system has a very high cost-effectiveness ratio, and especially the space-based GNSS-R can achieve high temporal and spatial resolution remote sensing of the Earth globally. Like traditional remote sensing radar technology, GNSS-R can be used for ocean altimetry, sea ice detection, sea surface wind speed, sea surface roughness, soil moisture estimation on the Earth’s surface, etc., and therefore has a very broad application prospect.