The modeling of plastic fuel tank systems for crash safety applications has been very challenging. The major challenges include the prediction of fuel sloshing in high speed impact conditions, the modeling of multilayer thermoplastic fuel tanks with post-forming (non-uniform) material properties, and the modeling of tank straps with pre-tensions. Extensive studies can be found in the literature to improve the prediction of fuel sloshing. However, little research had been conducted to model the post-forming fuel tank and to address the tension between the fuel tank and the tank straps for crash safety simulations. Hoping to help improve the modeling of fuel systems, the authors made the first attempt to tackle these major challenges all at once in this study by dividing the modeling of the fuel tank into eight stages. An ALE (Arbitrary Lagrangian-Eulerian) method was adopted to simulate the interaction between the fuel and the tank. The ALE method enables the sloshing phenomena to be simulated and allows vortices and cavitation to be captured. Blow molding simulation is conducted in the study to predict the thickness changes, as well as the residual stress and strain distributions in a multilayer thermoplastic fuel tank due to manufacturing processes. The information obtained was used as the initial condition in the crash simulation. An approach also has been developed to model the pre-tension of the fuel tank straps that was introduced in the fuel tank assembly process. The weight of the entire fuel system including the fuel is considered in this study to improve the modeling of the contact tightness between the fuel tank and tank straps. Validated by fuel tank sled tests, the proposed fuel tank modeling approach, incorporating the latest ALE method, manufacturing and assembly processes, and gravity effect, helps improve the correlation between CAE and physical tests significantly.