In order to prevent cascading failures in smart grids and secure the operation of power grid, from the point of view of the complex network theory, we developed a cascading failures model for understanding the robustness of a smart grid under targeted attack and the defense of its interdependent links. Furthermore, we analyzed the process of cascading failures using the theories of generating functions and percolation. The simulation results agree with those by theory analysis. It is also found that a smart grid can be more robust by improving the network connectivity density, reducing the pow...