Accurate and timely acquisition of the phenological information of winter wheat which is one of the main crops in China, is a prerequisite for its growth monitoring and yield estimation. Spaceborne Synthetic Aperture Radar(SAR) is an all-time and all-weather microwave remote sensing device, which can realize large-scale monitoring of periodic crop phenology. According to the time series Sentinel-1A SAR data, a phenological period identification method of winter wheat is proposed based on spaceborne dual-polarization SAR. This method uses eigenvalue decomposition and polarization scattering analysis to extract the backscattering coefficient, polarization entropy, scattering angle, etc., in different phenological stages to realize winter wheat phenology identification. The experimental results show that the overall accuracy of phenological phase identification reaches 79%. This method has practical value in winter wheat growth monitoring.