Area Replacement Rule and the method namely "design by stress analysis" in which Finite Element Method is used are adopted in the analysis of a cylinder vessel with 100-500mm openings and 1-6MPa internal pressures. In the process of stress analysis design, two paths noted as Path1 and Path2 are used in the stresses assessments. The results indicate that analysis by Path1 is relatively conservative by comparing to Path2 which is listed in the national standard. According to the results from Path2, reinforcement pad method is suitable for conditions in which internal pressure is below 6 MPa, and at a relative low pressure the safety margin is of a great amount for reinforcement pad method.