<p>Spacer fabric composites are widely used in wearable and flexible structural applications, while auxetic materials with a negative Poisson’s ratio offer unique deformation characteristics that can further enhance their functionality. This study investigates the mechanical properties of an auxetic structure–spacer fabric composite formed by integrating a rotating-hexagon auxetic lattice with a spacer fabric substrate. First, a parametric formulation of the rotating-hexagon geometry was used to design the auxetic lattice and achieve integration with the textile base, enabling the development of a composite with tunable deformation behavior. Then a generalized predictive model tailored for this class of auxetic structure–spacer fabric composites was established to quantitatively estimate the effective elastic modulus and Poisson’s ratio and to clarify the explicit relationships between geometric design parameters and the resulting mechanical response. Next composite specimens with various rotation angles were fabricated using parametric modeling and additive manufacturing. Finally, the effects of rotation angle and side length on the directional Poisson’s ratio and effective modulus were experimentally examined and compared with model predictions. Results show that the composite largely inherits the auxetic deformation of the rotating-hexagon lattice while gaining additional structural stability from the spacer fabric. The close agreement between experiments and predictions confirms the accuracy and applicability of the proposed model.</p>