Abstract: Friction stir lap welding assisted by friction additive (FA-FSLW) was proposed to solve the following problems during Ti/Al dissimilar friction stir welding process: low joint strength and wear of tool. This new technology contains the advantages of solid state welding, such as low heat input, thinner intermetallic compounds layer. This study selected 6082 aluminum alloys as the pre-deposition layer to assist the bonding between 3 mm thick 2A12 aluminum alloy and 4 mm thick TC4 titanium alloy plates. The tool was set into the 6082 deposition without touching the titanium surface. The joint with the maximum tensile load of 12.2 kN was obtained. The study found that the larger the interface offset, the lower the load bearing. The Ti and Al elements have undergone significant inter-diffusion during FA-FSLW process. The element of Si was segregated at the interface, and then metallurgical reacted with Ti and Al, to form a Ti-Al-Si intermetallic compound layered of nano-level, which established the foundation for high load-bearing of the joint.