Abstract: A three dimension mathematical model was proposed to calculate the temperature field during scanning electron beam welding.Adopting reasonable welding technology to obtain the large spot radius of electron beam,the simulations and experiments on scanning/normal electron beam welding of TC4 titanium alloy were carried out.The simulated results agree well with that of experiments.The research shows that electron beam scanning can increase the weld pool width,decrease the weld pool depth,make the weld pool being steady state earlier,and obviously decrease the maximum temperature and the cooling rate of the weld pool.For the electron beam welding process (U=60 kV,I_b=100 mA,V=0.9 m/min) with a 500 Hz ellipsoid beam scanning,the maximum temperature of weld pool can decrease by 1900 K and the cooling rate decreases by 100 K/s.