Mechanical properties of a 3D spacer fabric are determined both by mechanical properties of its components and its unique structure. However, at present, there is no well-received method to describe the mechanical performance of a 3D spacer fabric. In this article, numerical methods are used to analyze a compression mechanism of a typical 3D spacer fabric, as an example, based on features of its structure. Micro X-ray computed tomography was used to determine a precise geometry model of the studied fabric. To give a deeper understanding of the effects of the fabric's structure on its mechanical properties, the finite element (FE) method was used to simulate the compression process of the fabric; seven FE models were developed to simulate its compression behavior. Based on results obtained with these models, the compression mechanism of the 3D spacer fabric is summarized and the factors affecting it are determined. The same method of analysis can be extended to other studies of 3D fabrics.