We investigate the characteristics of dissimilar metals, such as TC4 Ti alloy/5052 Al alloy, joined via laser spot welding using a continuous fiber laser device of 1070 nm wavelength and 6 kW maximum power. Results indicate that with the same defocusing distance, two molten pools are formed during welding with a low laser power. Shrinkages, pores, and cracks occurred on the Al base metal. With increasing laser power, a part of the molten Ti flowed into the fusion zone, forming a nail shape, due to which mutual diffusion and reaction occurred between the Ti and Al atoms at the edge. TiAl2 and TiAl3 phases are produced close to the Ti and Al sides, respectively. A layer of TiAl3 intermetallic compound formed at the Ti-Al interface but not in the fusion zone. The TiAl3 layer became thicker as the laser power is increased. Joint strength first increases and then decreases with the increasing laser power at defocusing distances is less than +50 mm. The maximum fracture load is less than 3000 N. At the defocusing distance of +50 mm, two peak values of joint strength are observed with a variation of laser power. The fracture locations are distributed at the interface and the Al alloy base metal. Cleavage and ductile fractures are the corresponding forms of fractures. The maximum joint strength reaches 3571 N.