The 2015 Mw 6.4 Pishan earthquake is the largest to have occurred in the Tarim basin since 1976. It caused great damage to infrastructures and private houses in the city of Pishan and the surrounding areas. We use ascending and descending interferometric Sentinel‐1A (S1A) and Advanced Land Observation Satellite 2 data to constrain the source parameters of this earthquake. The coseismic fault‐slip model obtained from a joint inversion indicates that the rupture is dominated by a thrust motion with a 7 km buried depth. The fault slip is centralized on a roughly 30 km (along‐strike) × 15 km (down‐dip) rectangular asperity, with ∼1 m maximum slip at a depth of 11 km. The total seismic moment 5.6×1018 N·m, corresponding to a moment magnitude Mw 6.47, is slightly larger than the seismological estimate. The absence of fault slip in the upper 7 km of the crust suggests that this earthquake left an unruptured up‐dip fault under the city of Pishan. Both the coseismic fault‐slip distribution and the early postseismic deformation demonstrate that the S1A data have obvious superiority in monitoring earthquakes worldwide.