Abstract: The stability of the dual flexural-shear substructure system with different heights has been studied. First, the analytical continuum model is established, and the buckling equation of the dual system is derived, and the analytical solution for the critical load of the dual system is proposed. According to the interaction between the upper and lower parts of the dual system, the approximate formula for the critical load has been given. Comparing with the analytical solution, the approximate one not only has good accuracy but also is much easier to be applied. According to the research, we found that with the relative heights of two substructures varying, the total critical loads of the dual systems will change accordingly. And when in the case the relative height reaches the optimum relative height, which is not equal to 1, and the total critical loads will get the maximum value.