The paper proposes an approach to estimating the security of cyber-physical systems based on the modeling graph structural characteristics. As structural characteristics of the graph, indicators based on the spectrum of the graph were studied. To test the hypothesis about the negative impact of attacking influences on the structure of the graph, experiments were carried out, consisting in the sequential removal of vertices and edges from the graph with “small world” property. This type of graph was chosen because researches show that the “small world” property is inherent in high voltage smart grids. The conducted experiments showed that the attacking influences on the system, displayed on the graph, negatively affect the structure of the network, and therefore lead to inefficient information exchange and, consequently, the functioning of the system.