Abstract: Objective To explore a new method for finite element modeling to achieve material property assignment based on in situ CT gray value in simulated osteotomies for deformities. Methods A CT scan dataset of the lower limb of a patient with extorsion deformity was obtained for three-dimensional reconstruction using Mimics software and preparing a solid model. In the CAD software, the parameters for osteotomy simulation were defined including the navigation axis, rotation angle and reference plane. The tibia model was imported to the FEA pre-processing software for meshing procedure and then exported to Mimics. All the segments of the tibia meshed model were assigned uneven material properties based on the relationship between CT gray values and material properties in the Mimics software. Finally, all the segments of the tibia model, reference axis and reference plane were assembled in the pre-processing software to form a full finite element model of a corrected tibia, which was submitted to resolver for biomechanical analysis. Results The tibia model established using our modeling method had inhomogeneous material properties based on CT gray values, and was available for finite element analysis for the simulation of osteotomy. Conclusions The proposed finite element modeling method, which retains the accuracy of the material property assignment based on CT gray value, can solve the reposition problem commonly seen in modeling via the routine method of property assignment and provides an efficient, flexible and accurate computational biomechanical analysis method for orthopedic surgery.