The stability analysis of large space structures such as space solar power system is discussed in this paper. Because these structures are very large and flexible, the mutual interference among position, attitude and structural deformation cannot be negligible. Therefore, a comprehensive analysis of the system dynamics including position, attitude and structural deformation on orbit has been required. In this study, we propose a new method based on potential energy to estimate the integrated stability. Based on potential energy, the integrated stability of deviations in position, attitude and structural deformation on orbit is analyzed. The potential energy, which is caused by gravitational force and centrifugal force, is considered as well as strain energy of the structure. By using the potential energy, not only equilibrium states but also the degree of stability in the neighborhood can be estimated. As a case study, we focus on a solar-array platform with gravity gradient stabilization. At first, the stability about the position and attitude is estimated based on the potential energy. As compared with the numerical results of system dynamics, the validity of the estimation is confirmed. Then, we show the change of stability which depends on the satellite's configuration. Finally, the stability of structural deformation around the equilibrium point is shown through the potential energy.