A COPV (Composite Overwrapped Pressure Vessel) is consisting of a thin metallic liner wrapped with a fiber composite. The outer side CFRP layers bear the load due to internal pressure, and the inside liner provides a barrier between the fluid and the composite. Because of its high specific strength compared to metal pressure vessel, COPV have been applied to the field of aerospace. If it suffers impact load such as by falling tools, both CFRP and liner cause the impact failure, and a dent remains in liner by metal plastic deformation. Usually, the liner deforms elastically in MEOP (Maximum Expected Operating Pressure), but in the part of liner dent, there is a possibility of plastic deformation by adding the bending moment as well as the load due to internal pressure. If tensile and compressive plastic deformation repeats by pressurizing and depressurizing, the ratchetting plastic deformation occurs and plastic strain is accumulated in liner dent. This study discusses the ratchettig defomation of the COPV liner, and investigates the presence of ratcheting by FEM.