The influence of heat and force factors and their interaction, such as forging temperature, heat treatment process, deformation amount, on the element diffusion of Al, Nb, V at weld zone has been investigated for the Ti-24Al-15Nb-1.5Mo/TC4 dual alloy billet after welded in vacuum and rolled or treated. Investigations showed that the energy of atom motion can increase with the increase of deformation amount and heat treatment temperature, favorable for the elements diffusion and the homogenization of micro-hardness due to the change of shape and size for the grains and phases and short diffusion journey of fine grains at the weld seam. It is found that the concentration of niobium is high at the Ti-24Al-15Nb-1.5Mo side of weld seam. There are two reasons: one is niobium diffusion out from DO19 lattice when re-solidified during welding; the other is local deposit of niobium to fill up the vacancies when AI, Mo diffused out the lattice. The heat treatment route can affect the diffusion rate through changing the morphology of microstructure at weld zone.