International competition in the market to meet customer demand draws diverse manufacturers' interest in implementing cost-effective manufacturing processes to increase product quality and productivity. In the manufacturing world, most of the products are produced by casting process, and then we are constantly surrounded by objects that have come out of a mold. However, the quality of the moulded pieces is influenced by the surface quality of the steel mold. Even though different research papers have been carried out on polished mold steel and understand the material removal characteristics of fluid jet polishing mechanisms, their polishing processes are still incomplete and very little attention has been paid. This paper presents a computational fluid dynamics-based analysis of the material removal characteristics of fluid jet polishing on an SKD61 mold steel workpiece. Fluid jet polishing is a pre-mixed very fine free abrasive particle were propelled by liquid to impact on the surface of the workpiece. The effects of the key polishing parameters such as slurry pressure ,standoff distance ,impact angle and polishing time were studied. A computational fluid dynamics model was developed to simulate fluid flow and material removal characterstics . Material removal characteristics such as depth of cut were obtained with the help of analytical anvestigation in collabiration with the descrete phase model of Okai’s erosion model. After polishing is carried out in ANSYS FLUENT solver, Mountain SPIP lab measures the surface roughness of a mold steel. Proces parametres were also optimised making use of response surface methdology anlysis via a design expert software package. A surface roughness of (Ra) 0.838μm and a maximum depth of cut of 2.245 μm were achieved at a parameter setting of slurry pressure of 3.75 bar, polishing time of 49.32 minute, impact angle of 30° and standoff distance of 10 mm.The numerical simulation study showed that about 88.81% improvement in surface roughness from initially (Ra) 8 μm taken from prior experimental study to a final (Ra) of 0.838 μm has been achieved using optimal parameters as compared to prior experimental study. Keywords: CFD, Fluid jet Polishing, FLUENT, SKD61 Mold steel, Mountain SPIP, Response surface methodology.