Aiming at the problem that nail’s melting time in slab isn’t been taken into consideration for measuring method of solidified shell by nail-shooting technique, the mathematical model of heat transfer for nail in slab is built, and the process of nail melting in slab is simulated by the finite element software MSC.Marc. The revising method and formula are proposed. The differences 0.5% and 1.2% for solidification coefficient and solidification ending fore and after revising are analyzed by instance. It shows the calculation of solidification coefficient and solidification ending is more exact due to adapting the revised method.