Triangle heating technique using a gas flame is used to deform steel plate in ship construction. However, in the flame heating process, the heat source is often difficult to control and parts cannot be deformed efficiently. In this study, a numerical model is developed to study the triangle heating technique with the more controllable heat source of high-frequency induction heating and to analyze the deformation of steel plate in the heating process. To simplify the many complex trajectories of the triangle heating technique, a rotational path of inductor is suggested and then a 2-dimensional circular heat input model is proposed. The heat flow and transverse shrinkage in steel plate during triangle heating with the induction heat are analyzed. The results of the analyses are compared with those of experiments to show the good agreement. The heat source and thermo-mechanical analysis models proposed in this study were effective and efficient for simulating the triangle heating technique in the forming of steel plate in shipbuilding.