Abstract: The physical model of electron beam welding was established in consideration of all the thermal process and forces during electron beam welding. The molten pool behavior and weld shape of 304 stainless steel heated by stationary electron beam were studied by numerical simulation of the temperature field and fluid flow field. The results shown that the temperature gradient of top surface was higher than 10⁶ K/m and the peak temperature of the molten pool fluctuated at boiling point of 304 stainless steel. The reaction force of metal vapor was the main driven force during heating stage. The top surface was depressed due to the impact of metal vapor and shacked with time. The Marangoni convection caused by surface tension gradient became the main driven force during cooling stage due to the reduction of metal vapor reaction force in the cooling stage. The weld width at the top and bottom surface was large than the center of thickness direction. The weld width at the top surface, bottom surface and the center were 1.9 mm, 1.8 mm and 1.6 mm respectively.