Abstract: According to Fisher discriminant criterion,a new method whose discriminant coefficient and critical value change along with time was put forward and applied to forecast precipitation in July of the Zhengyuan observational station whose rainfall can mostly reflect the changing rule in Longitudinal Range-Gorge Region.Based on the former researches that pointed out Indian Ocean temperature distinctly influenced on the precipitation change over the region,a discriminant predictive equations were built with the former autumn,winter and spring zonal gradient of sea surface temperature anomalous.The application results indicated that the new method had efficient fitting and forecasting accuracy as well as better forecasting stability.