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Based on the principles of soilmoisture balance, the core of the model takes full account of the exchange relations of soil, atmosphere, and plant, with the forecast period being ten days. The cornfield soil relative humidity for every 10 days from 34 moisture measurement stations in Heilongjiang Province were used to represent that of the corresponding county. The soil relative humidity at the end of the last 10 days and the forecasted precipitation of the next ten days were used to forecast the soil relative humidity at the end of the next 10 days. According to soil drought indicators，the level of soil droughts/floods was determined, and a test was made with the observed soil humidity in the cornfields from March to November in 2007. The results show that the forecasts were more accurate in spring and autumn, with absolute errors being less than 5 percent; errors in summer were slightly higher than those in spring and autumn, with absolute errors being under 6 percents, even zero in some places. To use the determined levels of soil droughts/floods to test the forecasting accuracy of soil droughts/floods, the results proved satisfactory.