Polymer-derived ceramics (PDCs) are printable and tunable materials which have great potential to replace metallic materials in biomedical implants due to their good biocompatibility, light weight and high corrosion resistance. Additionally, the polymer-to-ceramic transition provides new opportunities for structure architecture design and property tailoring. Shaping at the polymer state using 3D printing allows the final ceramic products to exhibit arbitrary shapes and complex architectures that are otherwise impossible to achieve through traditional processing routes. This approach not only avoids the high cost and challenges in directly machining the hard and fragile ceramic parts, but also opens up new opportunities for customized biomedical implants that rely on complex 3D shapes and tunable mechanical and biochemical functionality. A multiscale computational model is developed to explore the phase transition mechanisms and their correlations with processing parameters and mechanical properties of the final ceramic product. Molecular dynamics simulations are carried out first to track the chemical reaction mechanisms and atomic structure evolution. The ceramic formation rate, which is predicted from the interplay between gas generation and gas diffusion, is transferred to the finite element model (FEM) for coupled heat transfer and phase transition analysis. FEM calculations concern the effect of pyrolysis temperature and heating rate on structure-level phase composition and mechanical response. It is found that there is a threshold of pyrolysis temperature above which full ceramic phase is formed. Higher heating rate promotes ceramization and leads to higher elastic modulus. In addition, volume shrinkage is found to accelerate ceramic formation which enhances material strength but can potentially lead to decreased toughness.