The integration between the information layer and the physical layer has become increasingly pronounced with the advancement of novel power system. Coordinated information-physical attacks pose significant threats to novel power system, resulting in substantial economic losses. To guarantee the secure and dependable functioning of the novel power system, this paper firstly analyzes the coupled mechanism of electro-gas coupling comprehensive energy information-physical systems and interaction between the information layer and the physical layer. By integrating game theory and the RAND risk assessment model, a three-layer dynamic game model considering joint attacks on the information layer and the physical layer is proposed. The game model is transformed into a mixed integer linear programming problem, using load loss as the metric to effectively determine the allocation of resources across different components. The validity of the proposed model and method is verified by an example analysis on the electric-gas coupling system composed of IEEE-30-node power grid and 11-node gas network.