Finite element model could be generated by computed tomography (CT) data set which provide accurate information about bone geometry and tissue density. In this work, an efficient approach for computing CT numbers for each element is presented. Mechanical properties of bone tissue can be estimated according to the relationship between tissue density and CT numbers. The experimental results show that this method can be applied to estimate mechanical properties of bone tissue accurately. The quality of meshes of geometry model and the number of materials are two key factors that affect the accuracy and efficiency of biomechanical analysis. In addition, the choice of relationship between CT numbers and elastic modulus should be proved by further study, which may help many researchers develop more accurate models.