Abstract: InSAR technology is based on a single satellite platform or orbit and can derive only one-dimensional deformation information of the landslide in the direction of the line of sight(LOS) of the radar satellite. It cannot derive the deformation along its aspect direction and cannot meet well the engineering requirements for landslide monitoring. To obtain more direct landslide deformation information of interest,we develop the model and algorithm for extracting the deformation velocity field of landslides in the aspect direction from ascending and descending Sentinel-1A data. Our method includes the following steps:(1)deriving LOS deformation velocity fields,(2)defining the slope-based coordinate system,(3)modeling the LOS deformation according to the configuration between the satellites and surface slopes and (4)solving for the displacements of landslides in the aspect and aspect-perpendicular directions with the assumption of no deformation in the slope surface-normal direction. We conduct a case study of an ancient landslide at Taoping Village,Li County in Sichuan Province and verify the accuracy of the model and algorithm through simulation experiments. The results show that,in contrast with the LOS deformation,the derived deformation in the aspect and aspect-perpendicular directions can display clearer deformation patterns and high-susceptibility areas. According to the results of the simulation experiments,the calculation error of the model and algorithm increases approximately linearly with the noise level. When the noise level reaches 10 mm·a^-1,the calculation errors of the deformation velocity field in the aspect and aspect-perpendicular directions are 14.1 and 11.9mm·a^-1,respectively. This proves the reliability of our method and results.