The line heating method is extensively applied to the bending of steel plate and the amending of distortion of welded members in fabrication of structures such as ships and bridges. Generally, in process of line heating, the surface of steel plate heated is quenched by water immediately after heating. Although there have been reported many papers concerning this line heating method, very few papers are dealing with the effect of water cooling on angular distortion. The authors carried out the experiments on the effect of water cooling on angular distortion in line heating of steel plate and performed the calculation of plastic behaviours of the plate being subjected to water cooling or air cooling subsequent to line heating by the using of total strain theory. In this investigation the following facts are clarified; 1) The quantity of angular distortion finally obtained in case of water cooling of the heated surface was less than that obtained in case of air cooling. 2) When the reverse side of heated surface was cooled by water after the temperature became distributed uniformly through section, the quantity of final angular distortion was more than that obtained in case of air cooling. The results of calculation used on total strain theory gave the rather reasonable explanation to the behavior of the plate line heated in the experiment.