In this paper, some key techniques about FEM surface mesh generation from multiple trimmed free surfaces are presented. The Advancing Front method is adopted and its kernel algorithm is given. A new method combining the parametric space method and direct 3D method is used during the surface calculation. As for the parametric space calculation to find an optimal 3D point, the Tangent Vector Inversion is presented so as to cut down iteration. Test results show this algorithm is quicker and more robust. The FEM mesh generated from large multiple trimmed free surfaces can be applied to finite element method directly.