Carbon-based composites are attractive materials for aerospace and defense applications requiring good ablation and thermal shock resistance, and stable thermomechanical behavior up to 2000°C. 3D carbon/carbon (3D C/C) composites have complex tri-orthogonal multiscale architecture, resulting in a nonlinear thermomechanical behavior under off-axis loading. This behaviour is thought to be mainly related to the possible degradation of interfaces and the resulting frictional sliding of interface cracks [1, 2]. Following [3], we propose a multi-scale approach to the modeling of 3D C/C in which the behavior of the interfaces is explicitly taken into account. For this purpose, we developed an ad hoc cohesive zone model based on [4], which considers potential damage and residual frictional sliding of interfaces be- tween different mesoscopic elements. Experimental observations using in situ push-out tests on half-cut specimens supported the development of the interface model. These push-out tests allowed us to directly observe the mechanisms behind the interface degradation process. We were able to demonstrate different interface behaviors between different variants of 3D C/C. They also allowed the in situ identification of the tensile separation laws of the cohesive zone through the use of digital image correlation. Eventually, we simulated the off-axis response of two 3D C/C variants using our multiscale approach, and we compared the results with experimental off-axis compressive tests regarding macroscopic response and local strain fields. As a result, we are able to quantify the extent to which the interface properties have an impact on the macroscopic off-axis behavior of 3D C/C.