Abstract: Considering that the cascading effects could lead to a large-scale traffic paralysis in road traffic networks, this paper simulates the dynamic behaviors under cascading effects triggered by the jam of a site, and then builds a new cascading failure model of road traffic networks. an optimization method is given to enhance the safety of road traffic network. Through the contrastive analysis of the simulation results, we find the effectiveness of the proposed evaluation method of the site importance. Simulation analysis results also indicate that this optimization method can largely improve the safety of road traffic system. And the proposed method has great application to strengthen the security of road traffic networks.