Water pollution accidents occur frequently and cause severe damage in recent years. The objective of this study is to build a model for simulating spatial-temporal change of pollutants after water pollution accidents. A Simulation System of Water Pollution Diffusion is developed in this study. A water pollution accident in Yuncheng City, China is used as an example. The results indicate that the pollutant moves from upstream to downstream with an increasing pollution area but a decreasing concentration. Moreover, spatial-temporal changes of the pollutant concentrations show the inverted-V tendency, where the concentration at a point in space increases then decreases through time. Finally, on the basis of the comparison of simulated concentrations of benzene with monitoring concentrations of it, Mean Absolute Deviation and Mean Deviation are computed to measure model error. The results show that Mean Deviation is -0.028 mg/L and Mean Absolute Deviation is 0.255 mg/L, whereas the data range from 0.001 mg/L to 28.104 mg/L. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.