The invention discloses a method and 
system for forecasting urban accumulated water by means of rainfall forecasts. The method comprises the steps that rainfall forecast information of a target city is obtained by means of a 
data interface of a meteorological department, and the rainfall forecast information is converted into rainfall duration data; 
simulation computation is conducted on 
surface runoff in the rainfall process and the drainage process according to the rainfall duration data and by combining urban drainage 
pipe point and pipeline data and geographical 
information data, and running status data of a drainage 
pipe network in the drainage process is obtained; calculation is conducted on the water accumulation process by means of a multi-source non-single depression accumulated 
water simulation method according to the running status data of the drainage 
pipe network and combination with surface elevation information, 
raster data of one surface accumulated 
water depth is correspondingly obtained by conducting calculation on each rainfall 
time step, all the 
raster data of the surface accumulated water depths of the whole rainfall duration process are obtained, and the surface accumulated water 
information data of each preset time is obtained, wherein the accumulated water 
information data comprises but not limited to the position, depth and range of surface accumulated water.