The passive Synthetic Aperture Radar with Global Navigation Satellite System (GNSS) employs GNSS satellites as transmitters and receivers mounted near the ground. Since GNSS constellations are designed for global, reliable and persistent operation, the most important advantage of such a system is the potential of permanent monitoring on the area which is overlooked by a fixed receiver. In the paper, an experimental prototype of GNSS-based SAR for the purpose of obtaining larger scene images as well as the development progress was introduced at the first place. And then a latest imaging experiment of GNSS-Based SAR for railway bridge was carried out and the image was obtained with high quality when it was firstly used for China Railway High-Speed (CRH) railway bridge imaging. The positive imaging result suggested that it is possible to achieve change information extraction using GNSS-based SAR for the further safety evaluation of CRH operation in China.