The microstructure evolution and super-diffusion mechanism of weld zone of TC11 and TC17 dissimilar titanium alloys after linear friction welding under different frictional pressures (22–47 MPa) were investigated. The joint microstructure was analyzed by scanning electron microscope, and the atomic concentration near the joint interface was analyzed by electron probe. Results show that the temperature in the weld zone exceeds the β-phase transition temperature, the temperature of the joint drops rapidly after welding, and the weld microstructure changes to a fully recrystallized microstructure. Super-diffusion of atoms occurs at the joint interface, and the diffusion coefficient of typical atoms is about 100 times higher than that of diffusion welding atoms. Within the experiment parameter range, increasing the frictional pressure can extend the diffusion distance of typical atoms.