The large 8.0 scale earthquake that occurred in Wenchuan, Sichuan province, China on May 12, 2008 caused huge damage to people's lives and property. Airborne and spaceborne remote sensing can be used accurately and effectively in almost real-time to monitor and assess earthquake disasters, providing an important scientific basis and decision-making support for government emergency command and post-disaster reconstruction. The high resolution, multi-band, multi-polarization, and full-polarization synthetic aperture radar (SAR) system and theories developed in recent years provide important data resources and the basic methodology for post-earthquake monitoring and evaluation. In this paper, the cities of Beichuan and Dujiangyan in the Wenchuan earthquake region are chosen as study sites. Using advanced high-resolution, multi-band, multi-polarization, and full-polarization SAR data, and applying urban building backscattering models and target backscattering and polarimetric target decomposition theory, the backscattering characteristics, polarimetric characteristics and texture features between collapsed and intact buildings post-earthquake are extensively compared and analyzed. Subsequently, a new SAR detection method for collapsed urban buildings is proposed from these characterizations. Preliminary results from comparisons between this method and high-resolution optical data show that the proposed method is effective and powerful in detecting collapsed urban buildings devastated by an earthquake.