A method based on magnetization is proposed to predict the induced magnetic field of naval vessels. We first deduce a formula to calculate the magnetic field in the internal region of magnetized objects from the viewpoint of magnetization，and then use the formula to define the point-function demagnetizing tensor and prove some properties of the tensor. Finally we use this formula to develop a new method to predict the induced magnetic field of naval vessels in a nonuniform applied field，and we call it the Magnetization Method，in which the point-function demagnetizing tensor is used. Compared with traditional methods，the magnetization method features low computational cost，high precision and manifest physical meaning. A numerical simulation of ship model verifies the method.