The knowledge of orthotropic material properties of composite layers is very important for mechanical design of machine structures from composite material. This information cannot be found in related professional literature therefore it is necessary to determine by measurement, by basic experiments of mechanics of materials. The paper presents a new 3D finite element layer model-cell based on the meso-structure of a textile composite layer, with which one shall be able to determine the material constants of an orthotropic layer. The applicability of the numerical layer model-cell and the accuracy of the numerical results are confirmed by experimental results. The numerically determined material properties of the layers are used at mechanical modeling and computation of complex, layered composite structures.