Abstract: TC4 pre-alloyed powder was prepared by the super-high-speed plasma rotating electrode process (SS-PREP). The effects of vacuum degassing temperature (320–470 °C) on the chemical composition, microstructure, and mechanical properties of hot-isostatically pressed (HIPed) compacts were systematically investigated. The results show that with increasing degassing temperature, physically adsorbed water and chemically bonded hydroxyl groups on the powder surface are effectively removed, leading to a pronounced decrease in interstitial hydrogen and oxygen in the HIPed compacts. Meanwhile, the native dense oxide film on the powder surface remains thermodynamically stable and does not decompose within this temperature range. After HIP consolidation, all compacts achieve full densification, and the microstructure consists of lamellar α, equiaxed α, and β phases. Mechanical testing indicates that a higher degassing temperature significantly improves the overall mechanical properties of the alloy. In particular, the specimen degassed at 470 °C exhibits the highest ultimate tensile strength, yield strength, elongation, and reduction of area. This improvement is mainly attributed to the cleaner powder surface, which promotes interparticle diffusion bonding and enhances metallurgical bonding quality. These results demonstrate that 470 °C degassing is the most effective condition for powder-surface purification and mechanical-property optimization, providing valuable guidance for industrial processing.