At present, doctors mainly use multiple two-dimensional images to diagnose the bone deformities of lower limbs. It is difficult to comprehensively observe the deformed parts from multiple angles, which is detrimental to detailed planning before surgery. Therefore, the Web development technologies, such as HTML5, JS, and CSS, are employed to independently develop an online auxiliary diagnosis simulation system for lower limb bone deformities in this study. Various required functions are implemented, such as online 3D modeling of lower limb bones and artificial joints based on DICOM images, 3D model browsing in an all-round way, dynamical display and comparison between DICOM images, auxiliary diagnosis tools (including measurement tools, gray scale transformation, detail viewing, and precise positioning), and patient information management. The system integrates open source architectures such as VTK, Cornerstone, and Three. It has the advantages of strong practicability, online sharing, and easy scalability, providing an efficient and powerful online auxiliary platform for the diagnosis of lower limb bone deformities and surgical planning.