Abstract: Range ambiguity to signal ratio (RASR) is a crucial index of spaceborne synthetic aperture radar (SAR) system. The cross-polarization RASR performance is deteriorated because the cross-polarization signal is interrupted by the co-polarization ambiguities in the traditional full-polarization SAR systems. A new working mode, full-polarization terrain observation by progressive scans(TOPSAR), is presented to improve the cross-polarization RASR performance of the full-polarization spaceborne SAR system. With the Radarsat2 like parameters, a full-polarization TOPSAR system and a traditional full-polarization SAR system are designed and their RASR performance are compared. The simulation results show that the proposed full-polarization TOPSAR mode can avoid the interrupt from co-polarization ambiguities to the cross-polarization signal, and it can efficiently improve the cross-polarization RASR performance of the full-polarization spaceborne SAR system.