Abstract: As one of land cover changing factors, urbanization effects greatly on the flooding water. From the mechanism analysis of urbanization action, it showed that urbanization changed notably the processing of produce and confluent water, so that decreased the ability of basin’s holding water, increased largely the confluent speed. The runoff coefficient distinctly grow up. This paper took the urbanization of Shenzhen City effecting the floodwater planning of Shenzhen River as an example, got the results that urbanization would increased the speed of over land and channel flow concentration, shorten time, increase the flood peak flux. As to the flood water encountered in 100 years, the concentration time in the controlling points of the stemflow would be curtailed by 15.4%~21.7%, correspondingly the flood peak flux increase by 11.8%~19.0%.