Objective　To evaluate the accuracy of volume ratio of osteonecrosis of the femoral head measured by special computer software.　Methods　Necrotic volumetric ratio was evaluated by two methods in forty necrotic hips (from twenty beagle dogs) induced by liquid nitrogen: firstly, volume ratio was confirmed by the volume percentage of the necrotic lesion and the entire femoral head measured using fluid displacement. Secondly, all dogs were subjected to MRI scan before operation, and the image data were transferred to Dicom format using Mimics software, for reconstructing the three dimensional modal of the osteonecrosis of the femoral head, and then, Geomagic process and Ansys division was used to analyze the volume ratio.　Results　There were no significant difference appeared between the results of fluid displacement （25.8±10.6）％ and the Mimic analysis（26.4±10.2）%.　Conclusions　As a new method, computer software is reliable for the accurate assessment of lesion size of ONFH.