Laser forming is a technology which can form sheet material such as steel and plastic by irradiating a laser beam on the surfaces of material. In the forming, it does not need costly dies and molds, and forming degrees of freedom are high. However, since the forming mechanisms are complex, complete forming technology for practical use has not been developed. The objectives of this paper are to explain phenomena of laser forming by experiments and FEM analysis and to develop a forming method of curved surfaces by laser forming. The phenomena are explained by the temperature change, stress change, and plastic strain change at a laser irradiation point which was obtained by FEM analysis. Line energy is proposed for explanation of laser forming phenomena to classify the forming mechanisms, and a method is proposed in order to form curved surfaces of sheet material by irradiating a laser beam on maximum and minimum curvature lines. The effectiveness of the method was verified by a basic experiment.