Abstract: The development and production of the steel plates used for X70M thin walled 11.91 mm line pipes are described.The exported plate used for X70M thin walled 11.91 mm×2 803 mm line pipes has been successfully developed through reasonable design of chemical composition, steel making process and heavy plate rolling process and by use of TMCP(control rolling+ACC) heavy plate rolling process.The reason that the yield strength ratio is out of limits is analyzed and the key factors with which the yield strength ratio will be controlled for thin plate are determined.The analysis shows that the distribution amount in the finishing passes will greatly impact the plate properties.The temperature drop of the plate will be increased when the plate becomes thinner with the screw down value reduced in the final finishing pass, which will cause the deformation resistance and dislocation density of the plate sharply increased and in turn to made the plate strength increased.The cooled grain size will be finer if rolling is done under lower temperature so the increasing degree of the yield strength is larger than that of the tensile strength, which will cause the yield strength ratio of the plate increased.