Abstract: The time-series synthetic aperture radar interferometry can reflect the deformation process of landslides effectively. On September 14, 2019, a landslide occurred in Tongwei County, Gansu Province. However, whether the landslide had occurred slow deformation before the disaster and the cause of the landslide are worth tracing and discussing. In this paper, based on the Sentinel1-A ascent/descent data released by the European Space Agency (ESA), the two-dimensional deformation characteristics and sliding factors before the Tongwei landslide in Gansu Province were analyzed by SBAS-InSAR technique. The results show that there is continuous deformation of the landslide from September 2018 to September 2019, and the deformation variable increases with the passage of time, so the landslide is not a sudden event. Before the landslide occurred, the maximum cumulative shape variables in the vertical direction and east-west direction were 18.25 mm and 32.85 mm respectively. Based on the results of the two-dimensional time series, the distance analysis and the comparative analysis of rainfall show that the Kushui River and rainfall are the two main inducements of the landslide. The InSAR traceback results further verify the application potential of satellite-borne radar interferometry technology in landslide detection, which is a powerful tool for landslide identification and early warning, disaster prevention, and mitigation.