Abstract: There exist kinds of damages and defects at active oil gas pipelines owing to the mis-installation,corrosion from harmful media,geological environment change,and sea water scouring,etc. It is important to evaluate the effects of above defects on the pipe strength,life-span and safety correctly for ensuring the operational safety of oil gas pipelines as well as avoiding economic lost and environmental damage. Some main oversea pipeline defect assessment methods are introduced in this paper and evaluated on their application scopes,as well as their assessment steps.