Abstract This paper studied the effects of the magnitude, the direction, and the release time of pre-tensioning stress on welding distortion and residual stress on thin steels for a ship in the pre-tensioning method above using the finite element method. It was found that pre-tensioning stress in the direction of weld path did not affect angular and longitudinal distortion but brought a decrease of 8% in the magnitude of welding residual stress which may affect the buckling strength. Meanwhile, pre-tensioning stress in the direction perpendicular to weld path resulted in a decrease of 40–60% in the magnitude of angular distortion. Also, when the pre-tensioning stress was released 60 min after the completion of welding, it had a decreasing effect of 10–20% more in the magnitude of angular distortion than when released immediately after welding.