The effects of potassium and rare earth (RE) on the mechanical properties and thermal physical properties of Fe-V-W-Mo alloy were researched. The results show that the hardness and hot hardness of modified Fe-V-W-Mo alloy slightly increase, impact toughness greatly increase by 41.82% and reach to 11.09 J/cm2. K-RE modification is able to increase the wear resistance and heat conductivity coefficient and decrease heat expansion coefficient. The mechanism that K-RE improved the properties of Fe-V-W-Mo alloy was analysed. Fe-V-W-Mo alloy roll modified by K-RE was manufactured by means of common centrifugal casting method, its service effect was very excellent in hot rolling steel.