In the variational equation of destable potential energies

the potential energies of external forces by using additional moments of flexure and moments of torsion and their correspondent curvatures of destable displacement and increment of torsional angle are represented. Through partial integration method and with the application of displacements and natural boundary condition for stress

we can get all order differential equations from variational equation of potential energy for spatial elastic instability. The one among them that we compute with is the spatial combination equation systems of method. In this way we can easily settle the problems of the thin-wall bar under forces and problems of spatial instability at the complex cross-section structure circumstance.