Abstract: The geometric relationship of the global navigation satellite system reflectometry(GNSS-R)and the factors which influence the geometry are analyzed in this paper.As the geometry of GNSS-R is the basis for its study and applications,establishing a reliable geometric model of GNSS-R helps to achieve the remote sensing applications using GNSS reflected signals.In this paper,an approximate geomeric optical model of GNSS reflected signals is established.The iso-range and iso-Doppler zones from the different path are analyzed and the iso-range line and iso-Doppler line are calculated and simulated.The changes on the annular zones over different parameters are further summarized based on the simulations.The satellite elevation angle and the altitude and the speed of the receiver are indicated to be the main reasons for the changing of the iso-range line and iso-Doppler line.At the end of each section, the valid range of annular zones and the method to improve delay-Doppler resolution are discussed.