Abstract: Because of the disadvantage of the artificial influence factors and bad timeliness in occurrence stage forecasting of Cnaphalocrocis Medinalis,a simulation and prediction system for Cnaphalocrocis Medinalis occurrence stage was built by Phenological Model,public weather information and web database.The study showed that the new method had the advantages of high accuracy and fine timeliness for the forecasting of Cnaphalocrocis Medinalis occurrence stage according to the investigated data from Tongzhou site in 2003-2012.The single sine with horizontal method had the high precision for forecasting and the average error was only 0.56 day during one generation of Cnaphalocrocis Medinalis,compared with a average error of 2.35 days by the method of effective average temperature.Our results suggest that the system should be popularized and applied.