In machining a parabolic shape workpiece

equidistant surface errors will be produced on the machined workpiece surface. This paper analyses and calculates this error. The minimal distance of theoretical curve is gained by the three-point method

and the mathematical model of all points of the lapping tool’s surface is established by the two-point method

which can be applied in calculating equidistance-curve error of all the conic of lapping tool. The simulation results indicate that equidistance-curve error of lapping tool changes from 0 to 0.7 μm

which can satisfy surface precision requirement of the most components. The maximal error of beginnings and ends of lapping tool is 0.624 14 μm

and the equidistant surface error increases with tool wearing and abrasives tool wearing and curvature of parabolid increasing. The results show the validity of this method.