Abstract: To meet the need by the market for large-sized,extra-long,heavy wall seamless steel tubes,the large-sized corrugated round steel ingot is developed for the purpose of producing large-sized seamless steel tubes with the rotary-piercing+pilger mill rolling process,a kind of direct formation technology. The ingot as designed features small wave crest and shallow wave trough,multiple edges,nearly-circular cross-section and small inner taper,etc. Moreover,for the manufacturing,certain technical measures have been taken,including low mould temperature,low hot metal over-heat degree,low cast speed and long retarded ingot-cooling time,etc. As a result,the chronic big problem of the ingot as being apt to develop surface cracking is tackled. The ingot as produced with the above said modification actions has been in possession of such advantages as compact microstructure,and small chemical composition deviation. And therefore,production manufacture of finished pipes with such ingots features uniform pipe structure,high yield and high cost-effectiveness.