The global and systematic coverage of Sentinel-1 radar images enables to characterize, by radar interferometry, surface deformations at the scale of large active fault systems. This represents considerable progress in fault monitoring and opens new perspectives in seismic hazard assessment. Our study focuses on the Yushu - Ganzi - Xian Shui He active fault system (YGX), one of the most seismically active left-lateral fault system on the eastern part of the Tibetan plateau, which contributes to accommodate the collision between the Indian and the Eurasian plates. We analyze in particular the present-day behavior of the Ganzi segment of the YGX fault system, which may represent a 350 km-long seismic gap, unbroken for the past ~120 years. To measure the interseismic deformation across the YGX fault system, we perform a time series analysis of 4 years of Sentinel-1 InSAR data, acquired along ascending and descending orbits, using the New Small Baseline Subset processing chain including the latest adaptations (Doin et al., 2011, Grandin, 2015). Our results are presented as mean velocity maps across the fault system and highlight creep process along different sections of the YGX fault system. We present here a spatial and temporal characterization of this creep, analyzing series of mean velocity profiles, derived from Sentinel-1 InSAR data. We also propose a preliminary block model analysis constrained from both InSAR and GPS interseismic surface velocities to discuss strain localization and rates at a regional scale in the light of the tectonic and geological evolution of this area.