This paper is devoted to the microstructure geometric modeling and mechanical properties computation of cancellous bone. The microstructure of the cancellous bone determines its mechanical properties and a precise geometric modeling of this structure is important to predict the material properties. Based on the microscopic observation, a new microstructural unit cell model is established by introducing the Schwarz surface in this paper. And this model is very close to the real microstructure and satisfies the main biological characteristics of cancellous bone. By using the unit cell model, the multiscale analysis method is newly applied to predict the mechanical properties of cancellous bone. The effective stiffness parameters are calculated by the up-scaling multi-scale analysis. And the distribution of microscopic stress in cancellous bone is determined through the down-scaling procedure. In addition, the effect of porosity on the stiffness parameters is also investigated. The predictive mechanical properties are in good agreement with the available experimental results, which verifies the applicability of the proposed unit cell model and the validness of the multiscale analysis method to predict the mechanical properties of cancellous bone.