Abstract: Simulation of welding process is considered as a major driving force of the development of welding technology in the 21 stcentury.It makes predictions of the physical phenomena,joint geometry,welding distortion and microstructure so as to partially replace the time-consuming and costly experimentation in the development of new welding procedures and shorten the development period.In this paper,a simulation model is developed for the MIG welding process.Systematic and finite-difference-based numerical algorithms are desiged to simulate the thermal,electromagnetic and metal flows.The characteristics of welding power source,electric arc and wire feed device are also integrated into the system.It will provide a mathematical platform for the further study on welding physics,microstructure,mechanical properties and workpiece distortion.Analysis has been also conducted to study the metal transfer,weld pool oscillation and electric response.Some conclusions that are difficult to obtain by using experimental and analytical methods have been drawn.