Taken the computer case as an example, dynamics modeling and analysis of a thin shell structure is presented in this paper. Optimization is implemented with the goal to reduce the vibration. Four proposals of optimal design are simulated employing the FEM software. Those proposals differ in material, shape, pattern and connectivity. Some especial techniques are used to build the three-dimensional model and to finish the FEM analysis. The dynamics characteristics of the computer case are then investigated in modal analysis based on the dynamics theory. The result is acquired by comparing the modal parameters of those in different proposals. A preferable model takes also the manufacturing and cost into account. The skeleton is universal to dynamics analysis and design of other thin shell structure.