Chemo-mechanical polishing (CMP) is a key technology for improving the surface quality of diamonds. To address issues such as oversimplification in existing flow field simulation models and difficulties in simulating flow fields within grooves, a novel simulation method combining a porous media model with a dynamic mesh model is proposed. A two-dimensional equivalent roughness model was established to obtain corresponding porous media parameters, with verification showing less than 5% error in pressure drop prediction. Based on the equivalent substitution of the porous medium for the wafer-polishing pad thin gap to obtain the polishing pad roughness within the gap, and based on the dynamic grid-driven simulation model of the groove structure to simulate the fluid motion, a three-dimensional simulation model is established. The results indicate that the presence of grooves reduces the flow velocity in adjacent regions, and an increase in the polishing pad's roughness significantly decreases fluid velocity within the porous media zone. However, near the wafer bottom surface and polishing pad surface, the boundary layer effect dominates, rendering the influence of roughness parameters negligible.