Compared　with　traditional　CNC　machines,　robot　milling　has　the　advantages　of　low　cost,　high　flexibility,　and　strong　adaptability,　providing　a　new　solution　for　complex　surface　machining.　However,　robot　machining　trajectory　planning　in　the　real　world　is　time-consuming　and　has　safety　risks.　At　the　same　time,　how　to　achieve　3D　visualization　monitoring　in　the　milling　process　effectively　is　also　a　challenging　problem.　Digital　twin　technology,　with　its　characteristics　of　multi-dimension,　high-fidelity,　virtual-real　fusion,　and　real-time　interaction,　provides　an　effective　way　to　solve　these　problems.　For　this　purpose,　the　paper　designs　and　implements　a　robot　milling　motion　simulation　and　visualization　monitoring　system　based　on　the　digital　twin　system　framework.　The　system　uses　the　Unity3D　platform　to　construct　the　robot’s　digital　twin　body,　designs　a　material　removal　algorithm　based　on　mesh　deformation,　and　establishes　a　milling　motion　simulation　model.　Through　virtual-real　mapping　technology,　the　system　establishes　a　bidirectional　communication　between　virtual　and　physical　entities　and　achieves　the　result　mapping　of　the　robot　milling　motion　simulation　and　the　visualization　monitoring　of　the　milling　process.　Finally,　the　motion　simulation　and　real-time　visualization　monitoring　of　the　milling　process　are　tested,　verifying　the　effectiveness　and　timeliness　of　the　system.　©　2023,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　London　Ltd.,　part　of　Springer　Nature.