Inconel 718, as a typical difficult-to-cut material, exhibits high hardness, high strength, and low thermal conductivity. The tool is subjected to significant cutting forces and high cutting temperatures during the cutting process, which not only accelerate tool wear but also adversely affect the dimensional accuracy and surface quality of the machined parts. The straight slot features are widely present in aero-engine components, and the surface quality after finish machining decisively affects the service life and overall performance of the parts. A comparative analysis was conducted on the cutting performance of single-pass and multi-pass finish milling processes when machining straight slots of Inconel 718. The effects of different process methods on cutting force, surface topography, and material removal rate were investigated through theoretical derivation and milling experiments. The research findings indicate that single-pass finish milling of straight slots can effectively reduce the peak cutting force and the duration of force application, minimize milling tool deformation, achieve superior slot wall quality and floor surface accuracy, and enhance machining efficiency. Single-pass finish milling demonstrates significant advantages.