Considering that the information flow demand in power communication networks is often unevenly fluctuating, especially when the communication system is incomplete, information links are prone to congestion or overload. However, in reality, when congestion or overload occurs, communication links do not immediately disconnect but rather have a certain degree of redundancy. Therefore, to explore the impact of communication link overload capacity on the power grid, this paper proposes a cascading failure model of cyber-physical power systems considering link overload in the information layer based on an improved percolation theory. Firstly, the corresponding information system topology is generated based on the actual power grid to facilitate the analysis of subsequent cascading failures in the coupled network. Secondly, by setting the initial fault in the information side and considering the link overload status, the failure situation of communication system links and nodes is analyzed. Then, based on the improved percolation theory, the survival status of nodes in the power grid is analyzed until the end of the cascading failure. Simulation results on the IEEE-39 node system demonstrate that considering the overload capacity of communication links can enhance the robustness of the power grid.