By use of water demand data from 2000 to 2010 in Ningxia, this paper extracted population,GDP,gross value of industrial output and precipitation as the main influence factors and analyzed the eight factors that affected water resources demond based on the principle component analysis method.Taking the main indexes as input samples，the paper set up BP neural network model and forecasted the water resources demands in 2011 and 2012 by use of the neural network of trained and tested.The result can provide scientific reference for plan and management of water resources in Ningxia.