A negative Poisson’s ratio honeycomb material has the characteristics of anti-conventional deformation behavior and high impact resistance, which is a new lightweight microstructure material with broad application prospects. However, most of the current research is still at the microscopic level and two-dimensional level, and little research has been carried out for three-dimensional structures. Compared with the two-dimensional level, three-dimensional negative Poisson’s ratio structural mechanics metamaterials have the advantages of a lighter mass, higher material utilization, and more stable mechanical properties, and they have great potential for development in the fields of aerospace, the defense industry, and vehicles and ships. This paper presents a novel 3D star-shaped negative Poisson’s ratio cell and composite structure, inspired by the octagon-shaped 2D negative Poisson’s ratio cell. The article carried out a model experimental study with the help of 3D printing technology and compared it with the numerical simulation results. The effects of structural form and material properties on the mechanical characteristics of 3D star-shaped negative Poisson’s ratio composite structures were investigated through a parametric analysis system. The results show that the error of the equivalent elastic modulus and the equivalent Poisson’s ratio of the 3D negative Poisson’s ratio cell and the composite structure is within 5%. The authors found that the size of the cell structure is the main factor affecting the equivalent Poisson’s ratio and the equivalent elastic modulus of the star-shaped 3D negative Poisson’s ratio composite structure. Furthermore, among the eight real materials tested, rubber exhibited the best negative Poisson’s ratio effect, while the copper alloy showed the best effect among the metal materials, with a Poisson’s ratio between −0.058 to −0.050.