On 21 May 2021, an earthquake struck Maduo county in Qinghai Province, China, which is the largest earthquake to hit China since the 2008 Wenchuan earthquake. In this paper, ascending/descending Sentinel-1 and advanced land observation satellite-2 (ALOS-2) synthetic aperture radar (SAR) images are used to derive the three-dimensional (3-D) coseismic displacements of this earthquake. We employ the differential interferometric SAR (InSAR, DInSAR), pixel offset-tracking (POT), multiple aperture InSAR (MAI), and burst overlap interferometry (BOI) methods to derive the displacements observations along the line-of-sight (LOS) and azimuth directions. To accurately mitigate the effect of ionospheric delay on the ALOS-2 DInSAR observations, a polynomial fitting method is proposed to optimize range-spectrum-split-derived ionospheric phases. Besides, the 3-D displacement field is obtained by an SM-VCE (strain model and variance component estimation) method based on the high-quality SAR displacements observations. Comparison with the global navigation satellite system data indicates that the SM-VCE method can significantly improve the displacements accuracy compared to the classical weighted least square method, and the incorporation of the BOI displacements can substantially benefit the accuracy of north-south displacement. Apart from the displacements, three strain invariants calculated based on the strain model parameters are also investigated. Finally, based on the accurate 3-D coseismic displacements, the source parameters of this event are inverted, revealing four slip asperities with the maximum slip of about 6 m concentrated around the hypocenter. The estimated seismic moment is 1.8×1020 Nm, which corresponds to a Mw 7.44 event.