Although lots of methods have been developed for the analysis of shear-lag effects of wide flange box girder, so far not many have very successfully achieved both computational efficiency and generality of computational model yet. This paper presents formulation and computation of a high order, high performance element of 14 node, 56 DOF for large box girder. The structural analysis program has been completed in Fortran on the formulation of element stiffness matrix of folded membrane theory. The shear lag effects under concentrated loading, uniform loading and triangular loading has been calculated by the program and accurate result has been obtained for the wide flange box girder. This indicates that the formulation for the high order, high performance element is reliable, and efficient for application to high accuracy engineering analysis of membrane structures.