Abstract: In order to improve the assessment accuracy of network security situation, a network security situation assessment model was proposed based on particle swarm optimization(PSO) algorithm and least squares support vector machine. Firstly, the parameters on the performance of least squares support vector machine were analyzed, and secondly the parameters of least squares support vector machines were selected using the PSO algorithm, and the model of network security situation assessment was given. Finally the simulation experiment was used to test its validity and superiority. The results showed that the proposed model can obtain more ideal results of the network security situation assessment.