In this paper, the possibility of just using general machine centres in one-pass milling process to finish an aluminium plate with the mirror surface roughness is studied. In particular, how to find the optimal setting of machining parameters is presented. In this optimization problem, to evaluate whether the surface roughness meets the average criterion of a mirror surface requires real cutting experiments, and it is desirable to find the optimal machining parameters using as few experiments as possible. The 'sequential neural network approximation method' was used to find the optimal machining parameters, including the spindle speed, feed rate, depth of cut, and number of inserted blades in the cutter to maximize the metal removal rate while the surface roughness meets the average criterion of a mirror surface.