Abstract: Refractory Mo alloys are critical candidates for extreme high-temperature applications, such as aerospace propulsion components and nuclear reactor plasma-facing materials. However, microstructural instabilities, particularly abnormal grain growth at temperatures exceeding 0.7T_m (melting point), significantly degrade their mechanical reliability. This study aims to elucidate the microstructural evolution mechanisms and grain growth kinetics of Mo-1.5W alloy in the ultra-high temperature range of 1 800-2 000 ℃. It specifically focuses on the synergistic interplay between second-phase particle evolution and crystallographic texture reconfiguration. The Mo-1.5W alloy was prepared via powder metallurgy followed by hot rolling. High-purity Mo and WC powders served as raw materials. The sintered compacts were hot-rolled at 1 150 ℃ with a total reduction of approximately 85%, resulting in a microstructure with strong deformation texture. Subsequently, the specimens underwent vacuum annealing at temperatures of 1 800, 1 900, and 2 000 ℃ for durations ranging from 3 to 100 minutes. The microstructural characterization utilized optical microscopy (OM) and electron backscatter diffraction (EBSD) to analyze grain size distribution, local misorientation, and texture evolution. X-ray diffraction (XRD) identified the phase composition. Furthermore, the study applied classical grain growth laws and Zener pinning models to calculate the kinetic parameters quantitatively. The experimental results demonstrate that the Mo-1.5W alloy exhibits pronounced non-uniform grain growth behavior. The grain size distribution follows a bimodal pattern, where a few coarse grains coexist with a fine-grained matrix. This phenomenon shows high sensitivity to annealing temperature. Microstructural analysis reveals that the evolution of Mo₂C precipitates acts as the governing factor. In the early stages of annealing, fine Mo₂C particles are dispersed within grains and at boundaries, providing a strong Zener pinning force that inhibits boundary migration. However, as thermal exposure continues, these precipitates undergo severe Ostwald ripening. They coarsen and redistribute from intragranular sites to grain boundaries, forming band-like structures. This morphological change leads to a non-linear and spatially heterogeneous decay of the pinning force. Once the local pinning force falls below a critical threshold, grains with specific orientations, particularly 100, selectively break free. These grains possess intrinsic kinetic advantages and rapidly consume the surrounding matrix, eventually dominating the recrystallization texture. Kinetic analysis shows that the grain growth exponent (n) increases from 2.9 at 1 800 ℃ to 4.0 at 2 000 ℃, suggesting that the dominant diffusion mechanism may involve different mechanisms. Additionally, the apparent activation energy (Q_G) decreases from 268.9 kJ/mol to 225.6 kJ/mol with holding time, indicating a shift from a non-steady pinning state to a quasi-steady state controlled by particle ripening. In conclusion, the abnormal grain growth in Mo-1.5W alloy stems from the instability of the pinning network induced by second-phase evolution. The study establishes a unified kinetic model that describes the competition between intrinsic boundary migration and external precipitate pinning. These findings provide a theoretical basis for optimizing the composition and determining the service window of molybdenum alloys in extreme environments.