Abstract: Lorentz force formula was obtained using two methods, and verified by the welding simulation. Two kinds of methods to solve the Lorentz force were deduced in detail, and numerical simulation of droplet transition and arc characteristics were conducted by ANSYS software. Additionally, distribution of radial Lorentz force, images of droplet transformation and isotherm of welding arc were analyzed by comparing the simulation results. Results show that the indirect method has much better effects on results of the numerical simulation, and the distribution of Lorentz force is more close to the theoretical analysis owing to the magnetic vector analysis compared to the direct integral method. The calculated arc has not been compressed effectively, and the neck of droplet has not been also shrunk without Lorenz force source terms. Furthermore, the indirect method has a wider application prospect.