Abstract: Described here in the essay are the development activities associated with the full-length normalization process for the large-sized L290N SAWL pipe. Also studied are the problems of commonly-caused weakening of elongation yield strength and tube deformation as staying with the tube that is subjected to the full-length normalization treatment after being UO-formed into a tube from the linepipe-purposed steel plate as mechanically-hot rolled. The study result reveals that after TMCP rolled,the L290N linepipe-purposed steel of the C-Mn-micro Nb composition system develops both the ferrite and the pearlite 2-phase structures,having obvious elongation yield strength platform which still remains after the elongation yield strength is remarkably reduced due to the normalization treatment;and the elongation property is barely effected by the cold-shaping process with the cold deformation rate no more than 1.0%. With relevant engineering practice,the Φ711 mm×15.88 mm and Φ914 mm×17.48 mm full-length normalized L290N SAWL pipes are massively produced with all the indexes concerning the mechanical properties and geometric dimensions up to the GB/T 9711—2017 Standard and relevant customer requirements.