Abstract: Elaborated here in the article are the Rotary Expanding Mill for the hot-rolled seamless steel tube,involving such aspects as the basic configuration,the process features,and the present application status,etc.Based on the rotaryrolling principle for the seamless steel tube,the major parameters of the deformation process are quantitatively computed and analyzed in view of the deformation theory and the rotary-rolling kinematics.Also briefed here in the article are the problems as staying with the rotary expanding rolling process.Moreover actions for improving manufacture of the largesized hot-rolled seamless steel tube are proposed.