The multi-layer pressure vessel generates the preload stress during the process of wrapping & clamping. The contact between the wrapped layers and the inner shell is the source of the preload stress. The contact mechanics model shows the primary mechanics relationship, and the contact pressure vessel causes the local settlement. The theory contact pressure has 5% error with simulation value. The experiment values of inner wall are coincided with the theory stresses, and the largest error between the theory and the experiment is below 16.3%.