Abstract: Since the construction of early industrial pipelines,construction of the oil/gas pipelines has been developed for more than one century. And from the first edition of the specification of API Spec. 5L for Linepipe as issued in 1928 up to the 44th edition thereof as publicized in 2007,it has been developed nearly eight decades. Thanks to continual amendments and revisions,the specification has been a prevailing international standard as used for steel linepipes for oil/gas transport pipeline service. The 44th edition of API Spec 5L was is-sued on October 1,2007,and became effective on October I,2008,being jointly publicized with ISO 3183: 2007(the 2nd edition ) as the equivalent thereto for the first time. Described in the paper is the development course of API Spec 5L as well as the latest development and changes of it.