The Overseas Crop Yield Forecast System was developed with the tools of Microsoft Visual Basic 6.0 under the Windows 9x/2000/NT platform. The system consists of such modules as data management, data processing, data calculation and analysis, average unit yield forecasting, planting area estimation, total production forecasting, etc. It can analyze the agrometeorological average unit yield, estimate planting areas, and forecast the total productions of American wheat, American corn, American soybean, Indian wheat, Indian rice, Brazilian soybean, Chinese rice, Chinese wheat, and Chinese corn. The system has a reasonable architecture and is easy to use and highly automatized. Taking American corn as an example, a description is made to this system. The biggest error of the total production forecasting of American corn from 2001 to 2004 is 8.4% (absolute value), and the average error is 2.4%. The forecasting is totally accurate for 2005. The average forecasting accuracy of the system is above 90% and it can meet the current demands of agrometeorological service.