Abstract: GM(1,1) model groups for predicting runoff amount of Heine River basin on northern slope of the Qilian Mountains are built up with grey system theory. The forest eco-environmental factors influencing runoff amount of Heihe River are analyzed, their connectivities are: precipitation≥0℃ accumulated temperature>forest eco-hydrological factors. The runoff amounts of Heihe River in 1989-2005 and their fluctuation trends are predicted, which provides scientific bases for rational development and utilization of water resources in industry and agriculture.