Abstract: As a new type of high-efficiency welding process, the magnetically controlled double-wire single-arc MAG welding has poor arc controllability and is easily affected by external interference during the welding process. Therefore, in this paper, a self-designed excitation device was used to apply a longitudinal magnetic field to the double-wire single-arc MAG welding for regulation. Based on the Maxwell finite element simulation software, the variation law of excitation intensity with excitation current was quantitatively characterized, and the distribution of magnetic induction lines and magnetic induction intensity at different spatial positions was obtained. Through welding process experiments, the variation law of welding arc behavior under different excitation parameters was studied, and the influence of the applied longitudinal magnetic field on weld formation and the geometric characteristics of the weld cross-section was analyzed. The research results show that the applied external magnetic field can effectively improve the straightness of the double-wire arc and the stability of the welding process within a certain range, thereby significantly improving the weld formation quality. The change of the applied longitudinal magnetic field mainly affects the weld penetration and weld width, and the two generally show opposite variation trends. When the excitation current is 1.5 A, and the excitation frequency is 80 Hz, the weld formation quality is the best.