The invention provides a 3D printing method utilizing a melting bed and a 3D printing system. The 3D printing method utilizing the melting bed comprises the following steps that A, based on predefinedprocess logic and technological process of each structural unit layer, the melting bed is utilized for casting molding to form a corresponding structural unit layer entity; B, the formed structural unit layer entities are stacked according to the overall shape of a workpiece; and C, aiming at the stacked structural unit layer entities, welding process is conducted. The 3D printing system comprises the melting bed and a movable casting head, wherein the melting bed comprises a plurality of mutually-separated forming cavities, and spaces of the forming cavities can be adjusted so as to form maximum size areas corresponding to all the structural unit layers; and the movable casting head is located above the forming cavities and can conduct two-dimensional translational motion in the horizontal plane. According to the 3D printing method utilizing the melting bed and the 3D printing system, energy resources can be improved substantially, the manufacturing efficiency is improved, and application and development of industrial scale are promoted fundamentally.