A novel composite structure with isotropic negative Poisson's ratio has been presented in our previous paper [1]. However, the previous study has only focused on the effects of random inclusions. In this work, an extended numerical study on the effects of materials properties and geometry features of inclusions is conducted in order to better understand the deformation mechanism and mechanical properties of this kind of composites. Using finite element method, the overall negative Poisson's ratio effects and mechanical properties of the composites are analyzed in terms of different factors including thickness and stiffness of inclusions with uniform and non-uniform struts. The structure optimization of the composites with better negative Poisson's ratio effect and mechanical performance are discussed based on the numerical calculated results. The study shows that the Poisson's ratio effects and mechanical properties of the composites are significantly affected by geometrical features, stiffness and boundary conditions of inclusions. ; Institute of Textiles and Clothing