Abstract: With special supporting structure for heavy loading, a bottom main drive spindle's breakage appears in strip production of the R2 roughing stand in a 2250 mm hot strip mill. Based on the Marc software package, a 3-dimensional finite element model was constructed to analyze the combined bend and torsion stress state of a bottom main drive spindle in the R2 roughing mill. Under different loading situations of torsion, bending or both them, the results of finite element analysis show that the stress in the special supporting area is greater 60% than that in other normal areas of the spindle in different computing cases. It is also shown that torque is the main reason leading to cracking and breakage of the spindle. The maximum stress in the main drive spindle supporting area after replacing original hollow structure with improved solid structure is reduced by 21%. The reinforced main drive spindle was successfully applied in production of the roughing mill.