AbstractThis work focused on the leakage of the composite pressure vessel with a structure consisting of an aluminum alloy inner liner, a composite winding layer, and an aluminum covering. Through applying the finite element simulation approach and leakage rate test, it was found that the average strain of the winding layer in the lap region at the pressure of 46 MPa is 0.0078. Additionally, the leakage rate of the covering adhesive joint was investigated by considering the deformation, revealing that the leakage rate increases with increasing test pressure. The leakage rate at the lap region with a length of 18 mm is 2.05 × 10−7 Pa·m3/s at 0.0078 strain decreasing by 1.46 and 2.31 times compared to those under 12 and 7 mm lengths, respectively. The leakage rate exhibits a strict inverse correlation with the length of the leakage path under a pressure of 0 MPa. Additionally, when the deformation remains below the critical strain threshold (approximately 0.6%), the relationship between pressure and leakage rate shows a linear positive correlation. When the deformation of the component exceeds the critical strain threshold, the leakage rate of the component is significantly affected by its deformation and an increase in overall deformation results in a greater increase in leakage rate. The relationship between the two exhibits a non‐linear trend. This work provides strong technical support for the leakage assessment of composite pressure vessels.Highlights Deformation of the pressure vessel was analyzed through theoretical and simulation approaches. Establishing the relationship between deformation and pressure in metal–metal lap structures. Leakage analysis for different metal–metal lap lengths and deformation conditions.