Abstract: The smart grid has gradually developed into a power-communication coupled network, where the power grid and the power communication network are deeply integrated. Failures in communication nodes can affect the power system through the coupling relationship, potentially triggering cascading failures in the coupled network. Therefore, identifying and protecting critical communication nodes is an urgent problem to be solved. First of all, based on the interaction mechanism of power-communication networks, a power-communication coupled network model is established, and a critical node identification algorithm considering coupling effects is proposed. Then, an attack and defense game model for the power-communication coupled network is developed. Based on the attack and defense game process of critical nodes in the coupled network, a population competition firefly algorithm is proposed to solve the game model. Simulation results show that the optimal protection strategy generated by the algorithm can reasonably allocate protection resources according to the importance of nodes, reducing the vulnerability of the coupled network under malicious attacks and ensuring the secure and stable operation of the power-communication coupled network to the greatest extent.