Abstract: The failure mode of a sagged plastic structure part was analyzed by a combination of the CAE simulation and laboratory experiments, and then an improving design was performed for this plastic structure part on the basis of the principle of failure analysis. Finally, the optimized design proposal was validated by a combination of the CAE simulation and experiments. The results indicated that the static stiffness, creep resistance and fatigue durability of this plastic structure part were improved by this optimized design, and its service life was also extended.