In modern wars， it is difficult for traditional air defense systems to effectively and economically counter unmanned aerial vehicle （UAV） swarm， and ground-based laser systems have become an important means of UAV swarm defense under the key area defense scenarios. Research on the deployment of laser systems will help give full play to their combat capability. Based on the power density concept， the damage model of ground-based laser systems to the UAV target flying at a uniform speed in a straight line is derived. A fitness function is designed to evaluate the advantages and disadvantages of the deployment scheme. Additionally， the particle swarm optimization （PSO） algorithm is adopted to provide the optimal deployment scheme under different specifications and quantities of deployable laser systems， and under different possible attack directions， heights， and speeds of UAVs. Comparison with the scheme of deploying all the laser systems in the center of the key area and of deploying these systems randomly verifies the correctness of the proposed scheme.