Abstract: Abstract; During transverse welding of titanium alloy thick plates, the molten pool exhibits asymmetric flow within the narrow gap groove due to the influence of gravity, which affects the weld formation. To improve weld quality, an innovative method was developed to achieve asymmetric lateral oscillation of the arc based on narrow gap tungsten inert gas (TIG) welding assisted by an alternating magnetic field. Compared to conventional magnetic-controlled narrow gap welding techniques, the asymmetric oscillation of the arc creates varying heat input on either side of the narrow gap groove, resulting in different temperature gradients between the molten pool and the sidewalls. This actively controls the asymmetric flow of the molten pool during horizontal welding. The study focuses on the effects of excitation intensity and frequency on weld formation, employing a high-speed camera to capture the flow behavior of the molten pool within the narrow gap groove. Results indicate that the symmetry of the weld and the degree of molten pool sagging decrease progressively with the reduction of lower excitation intensity, achieving optimal values at upper and lower excitation intensities of 5 mT and 2 mT, respectively. In contrast, variations in excitation frequency do not significantly impact weld symmetry but primarily affect the weld contact angle, with well-formed joints exhibiting symmetric upper and lower sections and a small contact angle at frequencies of 0.5 Hz or 1 Hz. Additionally, force analysis of the molten pool reveals different forces acting on the upper and lower sidewalls. Reducing the magnetic field intensity during downward oscillation of the arc can diminish the force that promotes the downward flow of the molten pool.