The Ti6Al4V alloy powder has been successfully prepared by the multi-stage deep reduction method. In this paper, the mechanism of the magnesium thermal self-propagating reaction in the process has been explored. The products were characterized by XRD, SEM, ICP and laser particle size analyzer. The results show that Al and V elements will enter the Ti matrix as a solid solution, causing the diffraction peaks to shift to high angles. The two reaction modes of "pre-sintering-reduction-sintering" and "reduction-sintering" are the main reasons for the difference in product morphology. The volume averageD[4,3] of self-propagating products is positively correlated with the combustion temperature of the system. The remaining Mg mainly exists in the form of complexes such as MgTiO3 and MgAl2O4. These ternary composite oxides can be decomposed by metal calcium in the deep reduction stage, and finally the Mg and O in the product can be reduced to 0.01wt.% and 0.24wt.%, respectively.