Abstract: The requirements and standards pertaining to wellbore integrity and wellbore barrier in the process of well completion were illustrated. Well completion operation commences after the well is drilled to the designed well depth and logged, and ends when the Christmas tree is installed, wellbore barrier is tested and the well is handed over to the oil production department. The establishment of well barrier by using well barrier elements to ensure the safety of well completion was described. Then, the function, structural elements and acceptance criteria of well barrier were explained based on 4 typical well completion graphs. Finally, the function of completion string and its structure and design in different production modes were expounded, and the casing load & casing design and its assumptions and the well control activity in the process of well completion and its procedure were described. In addition, the acceptance forms of 3 main barrier elements (i.e., completion string, casing and cement sheath) were listed in the appendix.