A network defense system must balance both security and stability. To enhance its risk control capabilities， a comprehensive risk assessment model for the network defense system based on the combination of game theory and weight assignment is proposed. The risk evaluation index system is established through literature analysis， expert surveys， and factor analysis. The subjective and objective weights of the evaluation indices are calculated using the continuous ordered weighted average （COWA） and the entropy weight method （EWM）. The optimal combination weights are determined using game theory， and the risk evaluation level of the network defense system is assessed using the fuzzy matter-element method. A case study of a local area network （LAN） project validates the model. The results demonstrate that the model is a useful reference for assessing the risk of network defense systems.