Yttria-stabilized zirconia (YSZ)-based abradable sealing coatings (ASCs) have attracted increasing attention in aero-engine sealing systems. However, their wear resistance at high temperatures remains a critical concern. In this work, two coatings with different unmelted nanoparticle contents (UNCs) were prepared by supersonic atmospheric plasma spraying (SAPS), and the influence of UNC on the high-temperature tribological performance of YSZ ASCs was systematically investigated. The microstructure, phase composition, and wear behavior of coatings were characterized using scanning electron microscopy, X-ray diffraction, and high-temperature tribological tests, respectively. The results showed that at a temperature of 1000 °C, changing the UNC significantly altered the friction coefficient and wear rate of the ASCs. For both coatings, wear behavior is primarily governed by abrasive wear, accompanied by extensive adhesion of wear debris. At elevated temperature, the unmelted nanoparticles act as weak regions within the coating. Under friction-induced shear stresses, they preferentially fragment and detach, which improves the abradability. These findings provide insights into the structural design of high-temperature ceramic-based ASCs.