It is difficult to measure mechanical strain in the vicinity of a moving weld pool owing to the complex solidification process. Computational modelling of the welding process provides an effective method to study the stress/strain distributions of the weldment. In this paper, the driving force to weld solidification cracking, i.e. mechanical strain versus temperature at the trail of a weld molten pool, was modelled with the three-dimensional finite element analysis procedure. The dynamic stress/strain evolutions that contribute to the formation of solidification cracking have been calculated in the cracking susceptible temperature range. In the mechanical model, solidification effects, namely deformation in the weld pool, change of initial temperature for thermal stress/strain calculation, were treated by means of a dynamic element rebirth scheme. Solidification shrinkage was also taken into consideration in simulation. The results of comparison between the calculated driving force and the experimental measurements of the material resistance predict the susceptibility of solidification cracking.