Abstract: In this study, a new random orientation, multi-particle and multi-size Ti-6Al-4V powder sintering model was established by molecular dynamics simulation. The effect of particle size distribution on sintering densification behavior was studied, and the mechanism of atomic diffusion, particle evolution, defect generation and evolution and microstructure transformation mechanism in vacuum sintering of Ti-6Al-4V alloy were revealed. In addition, according to the sintering densification mechanism of Ti-6Al-4V alloy, the Ti-6Al-4V alloy with a density no less than? 99.1 %, a tensile strength of 1033 MPa, a yield strength of 965 MPa, and a percentage elongation exceeding 20 % was prepared by metal injection molding by selecting the appropriate powder particle size. The accuracy of the model for studying the sintering behavior of Ti-6Al-4V alloy was verified based on the Electron Backscatter Diffraction(EBSD) test results. The microscopic sintering mechanism of Ti-6Al-4V alloy revealed by is of great significance for the optimization of sintering process and the regulation of microstructure.