Abstract: Based on the magnetic-control arc sensor model,the mathematical model of weld for thin wire submerged arc welding was established to track seam.By using the mathematical model,the variation of weld width at the transverse alternating magnetic field was studied.The influencing curve of excitation frequency and current on weld with was obtained by experiments,and the simulation results and that of experiments were compared.The results showed that the weld width increased with increase of excitation current and decrease of the excitation frequency.The simulation results are basically consistent with the experimental results,which verifies the correctness of the model.The studies will provide the necessary theoretical guidance for the designment and development of the magnetic-control sensor and seam tracking system for thin wire submerged arc welding.