During milling operation, the cutting forces will induce vibrations on both the cutting tool and the workpiece, which will affect the topography of the machined surface. Based on the Z-map representation of the workpiece, an improved model is presented to predicate the 3D surface topography along with the dynamic cutting forces during an end milling operation. A numerical approach is employed to solve the differential equations governing the dynamics of the milling system. The impact of cutting parameters such as the feedrate, the axial depth of cut and the dynamic characteristic of milling system on the surface topography is investigated by simulation. The all above can provide some instructive directions to the manufacturing engineers in determining the optimal cutting conditions of an end milling operation.