Abstract: Thanks to adjusting the roll gap of the 3-roll PQF mill,the average equivalent wall thickness that is less than or greater than the nominal specification,and in turn,the corresponding calculation formula is also obtained. Furthermore the wall thickness range that the mandrel is capable of producing,and meets the requirement for the additional tolerance of a certain product is determined,and then verified with the 294 mm and 369 mm passes of the Φ460 mm PQF mill. The analysis leads to the conclusion as follows,adjusting the roll gap will unavoidably cause the transversal wall unevenness of the steel pipe,and thus reduce the wall thickness accuracy;the greater the amount of roll gap adjustment,the more serious the unevenness of the wall thickness;and the smaller the wall thickness,the more obvious this negative effect will be;and under the condition that the roll gap adjustment amount is the same,the wall thickness unevenness with large-sized pipe will be more serious.