Abstract: A method of 3D model modification using freehand sketch with single stroke is proposed to improve the interactivity of the modification.Firstly,according to the mathematical characteristics of the 3D model,an object-space silhouette detection method is used to extract the concise and clear internal and external silhouettes by detecting the contour points and suggestive contour points.Secondly,an endpoint proximity criterion for stroke matching is introduced to get the part of the silhouettes intended to modify effectively.Finally,based on the correspondence between the stroke and the silhouettes to be modified,deformation parameters are calculated and used in Laplacian surface editing process to rebuild 3D model and finish the modification.The experimental results show that the proposed method enables the users to edit and modify the internal and external contours of the 3D model with single stroke effectively.