This study mainly analyzed the theory of the attack- defense game. Firstly, it analyzed the game theory, then established the network attack-defense game model (NADGM), analyzed its replicator dynamics equation, expounded the network security game algorithm, and built the simulation experiment's network system. It was found from the results that the model and algorithm designed in this study could reflect the changes in network security well. It was also found from the analysis of nodes in the network that the number of infected nodes in the network first increased and then decreased. In contrast, the number of recovered nodes increased gradually, and the proportion of the final damaged nodes was about 10%. The experimental results verify that game theory is useful in network security and can be further promoted and applied.