In recent years, with the development of additive manufacturing technology, it has become possible to print a variety of materials using 3D printers. 3D-printing FRP (3DP-FRP), a technology for modeling fiber-reinforced plastics (FRP), has been attracting much attention. 3DP-FRP is expected to play an active role in various fields due to its high strength and rigidity while being lightweight. 3DP-FRP is expected to play an important role in a variety of fields, as it has high strength and rigidity despite its light weight. In addition, it allows free expression of external shapes and fiber orientation, which was difficult to achieve with conventional FRP materials. However, due to the high degree of freedom, it is difficult to design 3DP-FRP, and it is currently not possible to make full use of its performance. Therefore, in this research, we are developing a mathematical method to optimize the design of 3DP-FRP.