Abstract: Titanium–tantalum (Ti–Ta) alloys are characterized by high strength, excellent high-temperature resistance, corrosion resistance, and outstanding biocompatibility, making them promising candidates for aerospace and biomedical applications. However, composition segregation occurs during preparation due to the significant differences in melting points and densities between Ti and Ta, which limits their further application. To investigate the origin of this issue, molecular dynamics (MD) simulations were conducted to examine the effects of nanoparticle size, shape, temperature, and pressure on diffusion behavior. The results showed that Ti atoms were the dominant diffusing species. At 1500?°C and 0?MPa, spherical particles with a diameter of 4?nm exhibited a shrinkage rate of 61%, whereas cubic particles showed a rate of only 23%. Under the same temperature and pressure conditions, increasing the particle size from 4?nm to 8?nm reduced the shrinkage rate from 61% to 50%. At 0?MPa, raising the temperature from 1000?°C to 3000?°C increased the shrinkage rate of 4?nm spherical particles from 10% to 95%. At 1500?°C, increasing the pressure from 0?MPa to 200?MPa enhanced the relative density from 41% to 89%. These findings indicate that temperature is the predominant factor influencing diffusion behavior. Furthermore, both the diffusion coefficient and the extent of diffusion increased with rising temperature and pressure. The results of this study provide a theoretical reference for the preparation of highly homogeneous Ti–Ta alloys.