Abstract: To extract mid-surface from thin walled B-rep solid model,a novel approach based on wireframe mapping is presented.Firstly matched face pairs are searched,and a wireframe topology graph between matched faces is constructed.Then trustable 3D boundary loop using middle-curve algorithm is generated.One face from face pair is offset and verified using 3D boundary loop.If any boundary edge can match same edge in offset face's edge,the offset face as mid-surface is output.Otherwise,a mid-surface by 3D boundary loop is created using N-Side surface method.Finally all midsurfaces are stitched into a shell model.Experiments show that mid-surface can be quickly and robustly created from real complex model,and it make convenient the following surface meshing for finite element analysis.