The approach for forecasting relative humidity for cities by Modified Direct Model Output(MDMO)is presented.The MDMO is not a kind of statistical means and does not use any historical data from the numerical weather prediction model or from the observation.The M-DMO forecast is based on the 2-meter relative humidity forecast on grids form model T106,which is the current operational model in National Meteorological Center of China and developed from the previous model T63.The relative humidity forecast for 264 cities across China is made by computer going through reading the model forecast into the M-DMO system,interpolating in nonlinear formula the forecast values from grids onto cities,reducing the systematic errors of the model forecast,and modifying the difference in relative humidity between the maximum and the minimum on the initial day.The final relative humidity forecast checked and revised by weather forecaster on duty for the ten specific cities including Beijing,Shanghai,and Hong Kong has been shown on CCTV at night every day since June 20,1996.