Abstract: The spatial distribution of the arc current density is one of the key factors for revealing the thermal-force coupling in the welding process which determines the metallurgy and forming quality. A method to measure the spatial distribution of gas tungsten arc (GTA) current density was proposed. The GTA images acquired by monochromatic imaging were analyzed to calculate the temperature field using the Fowler-Milne technique, and then the spatial distribution of the current density was obtained by solving the partial differential equation of electric potential with the constraints such as the relationship between temperature and conductivity, the corresponding boundary conditions and the current conservation conditions, and so on. The result has good consistency with the data measured under the same experimental conditions in literature. The proposed method is able to measure the spatial distribution of the GTA current density in a non-invasive way, and therefore provides a basis for techniques of real-time monitoring and quality control of the welding process.