Abstract: Based on double ellipsoidal power density distribution heat source model, the effect of different mesh sizes on computational accuracy and efficiency of temperature field in Q345E plate butt welding was numerically simulated with ABAQUS finite element software. Combining numerical integral calculation, the difference of heat input between theoretical and actual results was compared, and then a suitable mesh size was proposed. The results show that with the reduction of mesh size, the convergence time and CPU computing time increased, the maximum value of weld temperature field and the width and depth of weld pool decreased. When the mesh size was reduced to 1/2 of length in depth direction of double ellipsoidal model, the difference of heat input between theoretical and actual results was relatively small, and the highest weld temperature and the width and depth of weld pool tended to be constant.