Embodiments relate to devices and/or methods for measuring three-dimensional contact stiffness of spur gear based on rough surfaces. A hexagonal mesh is used for partitioning, and areas of each square meshes are identical with respect to tooth surfaces. The embodiments include calculating contact pressure distribution of smooth tooth surface based on a finite element method and extracting node pressure of contact area Pi; and calculating contact stiffness of gear surface. Measurement herein is more precise and avoid disadvantages generated by hertz theory and the free-sliding interface. Gear stiffness properties and calculation methods are influenced by roughness parameters during rough tooth surface contacting processes. The embodiments use a finite element 3D contact stiffness calculation model, which is more accurate than former 2D calculation model or calculation formula. Errors associated with fabrication and manufacture processes are considered to makes gear contact stiffness more accurate and to establish the foundation of gear dynamics.