The current underground piping inspection method is according to the ”API 570 Piping Inspection Code” which is developed for petrochemical and chemical processes. As the outer surface of underground pipe line may suffer sever corrosion by soil, and for its unaccessable characteristics, the inspection method of underground piping is quite different from other processing pipings, so that it was issued as an independent section in the API-570 Code. This review paper focus the non-destructive inspection methods from the API-570 and other non-mandatory referent practices such as NACE RP-0169,NACE RP-0274,NACE RP-0275 and API-651.