Heat-resistant steel F91, which has high heat-resistance, is widely used in valve and pipe manufacturing industry, but it is difficult to process due to its high strength and toughness. To investigate the influence of cutting parameters on the machinability of F91, a series of milling experiments based on uniform design were carried out. From the experimental data, an exponential model of milling force was set up. The result of regress analyse showed that the model had a high confidence degree. A group of optimized cutting parameters were obtained from the model for dry cutting with TiAlX coated carbide milling cutter. Cutting with the optimized milling parameters, lower milling force, higher material removal rate and less tool wear could be obtained. The prediction model showed a satisfactory agreement with those obtained from the experiments, so it can be referenced in actual processes for F91.