To improve the efficiency of auto-body design, an algorithm of morphing design for auto-body based on free form deformation and isoparametric transformation was proposed. In this algorithm, the control finite element model (FEM) model was consisted of a collection of polyhedral elements, such as hexahedron, pentahedron and tetrahedron. Then the correspondence of isoparametric transformation between FEM model and control parametric volume was established, and the deformation of control parametric volume was propagated to the embedding FEM model. The algorithm avoided the problem of computational cost of the parameterization of local coordinates through the given isoparametric transformation and its inverse transformation. From the numerical simulation on FEM model of an auto-body, the validity and efficiency of proposed algorithm were verified.