Abstract: The filling process of weld metal in multi-pass and multi-layer welding was simulated by being activated layer-by-layer,and the finite element model of multi-pass and multi-layer welding for thick X70 steel plates with different thickness by using semiellipsoid heat source model and uniform cylinder heat source model to describe the arc and metal droplet heat sources,respectively.The evolutions of welding temperature field and stress field and the state of welding residual stress were simulated and analyzed.The results indicate that,the residual stress in weld after multi welding heat cycles has the similar state with that in HAZ.The residual stress at the weld root is higher than that at the weld toe of cosmetic bead.The difference of thickness between thick plates has few influences on the residual stress at the weld root of root welding,which reaches up to 468 MPa,and the residual stresses at weld root and weld toe are lower that the yield strength of the base metals.The simulated results is in good agreement with the experimental results,which indicates that the founded model has high reliability and accuracy.