Abstract: CAD surface segmentation plays a significant role in engineering fields.The research to date has mainly performed segmentation based on a single attribute,thus suffering from little applicability to different segmentation situations.We present a surface iso-segmentation method focusing on user-defined conditions designed beforehand according to the segmentation problem and relevant attributes.Based on user-defined conditions,the boundary point(BP)is calculated and searched in the growing direction of a boundary curve(BC),and then used for constructing the BC by spline interpolation.By constructing the BC of the input surface and its sub-surfaces,the input surface can be divided into several iso-surfaces.To ensure the generality of segmentation,a precise calculation method for the initial BP and the BP of sampling units on the parameter domain is explored.Finally,attributes including machinability,normal and curvature are used to design conditions for the iso-segmentation of several CAD surfaces,and in the machinable region segmentation test,the average BP deviation of our algorithm is 96.98%lower than that of an existing algorithm.Test results show that the proposed algorithm suits for various segmentation problems,and can achieve more precise segmentation.