Abstract: Factorials design and uniform design are applied in the high-speed end-milling experiments of ultra high strengthalloy steel （hardness>50 HRc, tensile strength σ_b>1.4 GPa）. Characteristics of this difficult-to-cut material in high-speed cutting process are analyzed and a nonlinear model on the relationship between the cutting force and cutting regimes is proposed. Experiments indicate that under the conditions of high-speed cutting of ultra high strength alloy steels, the interaction between depth of cut and feed per tooth, the interaction between width of cut and depth of cut, and the interaction between width of cut and feed per tooth are among the statistically significant effects on the cutting force. Relationships between cutting forces and cutting regimes are nonlinear, scale effect of the cutting parameters is significant; effect of a cutting parameter on the cutting force is sensitive to the choice of other cutting parameters.