Abstract: This paper presents a method for cubic NURBS representation of arc and circle,and puts forward ready-made results under different circumstances.In the method,an arc having central angle less than 180° is represented by a segment of NURBS curve determined by four control points,for an arc having central angle greater than 180°,two segments of NURBS curves are used for the representation.When the central angle equals to 360°,the circle representation can then be obtained.The method described in this paper is simple and consistent,and meets the demands of arc NURBS representation.