Most rapid prototyping machines accept the .STL format as the universal format of the geometric model, where the substance of the .STL format is essentially a triangular model. A partial replacement of the meshes in such a model is practically necessary, but has been received little attention. The purpose of this study is to develop a partial mesh replacement technique for replacing a region of meshes along a closed region of profile. The proposed method is primarily composed of three steps: cutting path computation, mesh segmentation and mesh stitching. The cutting path computation is employed to evaluate the intersecting points of all meshes lying under the projection of the boundary curve. Mesh segmentation is employed to divide the original meshes into two parts: preserved and replaced meshes. Mesh stitching is finally employed to sew the boundaries of the preserved and new meshes. Several examples are presented to demonstrate the feasibility and application of the proposed method.