Sandwich panels, for example, honeycomb structure, are widely used in various stages because they are lightweight and have high stiffness. Recently, an origami structure called truss core panel (TCP) has become known as a lightweight structure that has the same bending stiffness and better aspects in shear strength and in-plane compressive load than honeycomb panel. However, there are some difficulties in forming the TCP in general. In this study, a new forming process for TCP based on origami-forming is developed. In particular, the TCP is partitioned into several parts that can be developed into 2D crease patterns. After that, blanks of material are cut in the shape of these crease patterns and are formed by a robot system to get the desired 3D shape. In this paper, a partition method by dividing the TCP into pyramid cells and sheet plate is presented, which allows for the manufacture of a wider range of structure than before. Tool arrangement for a robot device and a countermeasure for springback are considered. By applying an origami unfolding technique, an improvement in the partition method is proposed by dividing the TCP into cell rows, and then searching for a crease pattern in order to fold that cell row. The cutting method of every cell is modified to reduce the number of facets, thereby simplifying the process. Finally, a crease pattern based on this new cutting method is presented for producing cell rows with any given number of cells.