In response to the issues of shallow TIG arc penetration and low welding efficiency in medium-thickness titanium alloy arc welding, TIG welding experiments were conducted on 6 mm-thick TC4 titanium alloy. The effects of different arc modes (direct current, low-frequency pulse, and low-frequency plus high-frequency dual-pulse) on the weld pool and weld bead formation were studied. Finite element simulation was employed to investigate the temperature field and flow field dynamics of the weld pool in dual-pulse welding, and the deep penetration mechanism of dual-pulse TIG welding was analyzed. The results show that compared to constant current and low-frequency pulse modes, the dual-pulse current mode increases the flow velocity of the weld pool, effectively excites the deep penetration keyhole at the center of the pool, promotes the downward movement of the heat source, and thus increases the penetration depth. The tensile strength of the dual-pulse TIG weld joint reaches 964 MPa, the joint strength coefficient is 98%, and the post-fracture elongation is 3.7%, achieving a near-equal strength match for the joint.