Abstract: According to the artificial influence factors and bad timeliness in rice insect control decision, a WebGIS based system for the simulation and forecasting of rice insect was constructed.The system included the simulation module for the insect stage that based on the function of degree-days calculating, that could automatically forecast the occurrence stage of insect;the real-time weather information including the temperature and humdity could remind the users the suitability of the weather for the pest prevalence, then provide decision support information for the guest;and the pest information showed based on WebGIS could help the user to decide the control tactics for the large-scale field, corrected the error decision.In 2012, the system forecasted the occurrence condition of for SBPH, WBPH, BPH and the rice leaf-roller successfully in Jiangsu province and then the IPM methods to control the pest were applied.The system was based on the structure of Apache+PHP+MySQL+MapServer, it was easy for the guest to use, and it provided the powerful tool for the management of standard and information pest data, precision control and support for pest forecasting.