The progressive failure analysis of composite pressure vessel under hydrostatic pressure has been carried out. The composite pressure vessel has been modeled by using layer structural shell element. After the failure of the weakest ply, the stiffness is reduced by either fiber failure or matrix failure. The stiffness of failed element has been totally discarded and other element are considered to remain unchanged after the weakest ply failure. The stress of the laminate at the same point is evaluated again to see if the laminate can carry additional load. This ply-by-ply analysis progresses until the ultimate strength of the pressure vessels is reached. A parametric study has been done on the progressive failure analysis.