In complex adaptive system (CAS) , the complex behavior of system is emerged from the bottom , that agents′adaptability bottom-up the complexity of the entire system. This idea can be simulated by the method of com2 puter aid simulation. Swarm is such a tools kit based on the bottom-up modeling method that can be used in CAS simulation on computer. This paper developed a Swarm based platformfor the simulation of complexity in spatial and temporal evolvement of flood disaster. Its application is illustrated with a Swarm based model and program for simu2 lating flood spreading. Some rules have been elicited from the experimental results ,which could provide useful infor2 mation for the disaster reduction and management .