W-based alloys play an indispensable role in various fields, such as aerospace and nuclear industries. However, their thermal stability decreases with grain structure refinement, limiting their high-temperature applications. Although certain solute elements can enhance thermal stability through phase separation or grain boundary segregation, a systematic research on the extent of grain structure stabilization and the mechanisms of multicomponent addition is lacking. Herein, ultrafine-grained W-10Cr and W-5Cr-5Sc alloys with uniform grain structures and similar average grain sizes were prepared. The thermal stabilities of these W-based alloys were systematically investigated to elucidate their stabilization mechanisms. Results indicate that sudden grain growth occurs at approximately 1300 ^oC in W-10Cr and W-5Cr-5Sc alloys, representing an increase of approximately 200 ^oC compared with pure W. Kinetic analysis shows that the grain growth index and activation energy for grain growth are minimized at temperatures corresponding to thermal destabilization. Moreover, the grain growth indices of W-10Cr and W-5Cr-5Sc alloys exceed those of pure W during thermal instability. Furthermore, beyond the thermal destabilization threshold, the grain growth rate of the W-5Cr-5Sc alloy was lower than that of the W-10Cr alloy. The addition of Sc modifies the Cr distribution in the alloy. In the W-10Cr alloy, the high-temperature stabilization mechanism of the grain structure was attributed to the precipitation of Cr-rich phases and the segregation of Cr at the grain boundaries. By contrast, the stabilization mechanism in the W-5Cr-5Sc alloy shifts toward the precipitation of Sc-rich phases along with the simultaneous segregation of Cr and Sc at the grain boundaries.