Abstract: Based on the calculated results of finite element analysis and given the pit size, the criterion of safety assessment for in-service pressure vessels containing defects suggested by China was applied to assess the surface pit in penstock.The assessment wes carried out according to the CTOD (crack tip opeaning displacement) test result.Different assessment methods were used according to the pit distribution.The assessment results indicated that the assessment points are located within the safe region defined on the failure assessment diagrams.So the surface pit can be accepted.