The edge effect appears at the edge of workpiece as a result of the uneven distribution of pressure in computer controlled optical surfacing (CCOS) and this restricts the fabrication accuracy in practice seriously. The edge effect has become one of the urgent problems of numerical control machining technology. Theoretical simulation and experimental verification are done based on liner pressure distribution model and skin pressure distribution model. The experimental results show that when the distance between the workpiece and the tool borders is relatively large (the distance is 1/3 of aperture of removal function in experiment) or short (the distance is 1/24 of aperture of removal function in experiment). Little difference between removal functions based on both of the models is observed and the effectiveness of the models is proved that when the distance is medium(the distance is 1/6 of aperture of removal function in experiment), the removal function based on linear model is closer to the experimental result and the skin model has a biggr deviation with the experiment result in the central area.