In this paper, water pollution diffusion is simulated and analyzed by information and visualization technology during water pollution emergency events. A simulation and decision support system for water pollution based on WebGIS is proposed to represent and manage data in two-dimensional network environment. Data is the key part of the system,including data acquisition, transmission, simulation analysis and application. In this system, the visualization and interactive application of two-dimensional diffusion models of water pollution and simulation result are researched in emphasis in the Internet environment. A section of the mainstream Yangtze River is taken as the experimental region to test the effectiveness. Experimental result proves that the system could effectively support the automatic monitoring and decision-making of water pollution emergency events.