Butt welding experiments on 1.5 mm thick TC4 titanium specimen are conducted by using 4 kW fiber laser. The specimen is jointed 0.08 mm aluminum foil in the intermediate layer. The optimal weld shape can be attained by adjusting craft parameters. The shape, metallographic structure, tensile properties and microhardness on welding joint are discussed. It is shown that better welding joint and stronger tensile strength can be achieved by adding aluminum foil in the intermediate layer of TC4 titanium specimen. Microhardness is dramatically stronger in the weld pool with TC4 titanium and aluminum foil than that in the weld pool with only TC4 titanium. The difference is about 90 kg/mm2. In the weld pool with TC4 titanium and aluminum foil, grain is much smaller, and the acicular α′ structure is tiny, and the metallographic structure is in net distribution. Besides, the two kinds of welding joints in the heat-affected zone have almost the same microhardness and microstructure.