In general,water quality time series not only has stationary and periodicity characteristics,but also has obvious multi-scale features. To improve the precision of the traditional autoregressive models,which were once widely used for forecasting water quality,the autoregressive model combined with the multi-scale wavelet analysis theory is proposed as a new forecasting model called WAR( Wavelet Autoregressive Model). Finally,this new method and the traditional autoregressive model are applied to predict fou...