Abstract: Risk assessments of wellbore integrity of conventional oil and gas wells are predominantly performed in one certain working condition at one specific time without systematic risk assessment method for wellbore integrity of oil and gas wells throughout the well life cycle.To correct the deficiency,systematic and quantitative assessment techniques were proposed for drilling,completion,production,plugging and abandoning. Thus,four kinds of conditions in the whole life cycle of oil and gas wells and they constitute a comprehensive evaluation of the wellbore. In this way,systematic risk quantitative assessment models and evaluation indicatorsfor oil and gas wells wellbore integrity were established.Risks in wellbore integrity in the whole life cycle of the Puguang Gas Field were estimated by using aproposed risk assessment method. Assessment results showed that the integrity of the wellbores in the field were operating at a higher risk level and it was verified with actual conditions on site. Research results showed that wellbore integrity evaluation method can evaluate the risk of wellbore integrity in the whole life cycle of oil and gas wells,and can provide valuable references for minimizing the risk of wellbore integrity of oil and gas wells.