Abstract: This paper, through positioning observation of sand-fixation windbreak systems in Gaotai region of Heihe River valley, analyzed changes in ecological effect of sand-fixation forest in recent 20 years. The analysis reveal following results: With regard wind prevention and sand-fixation, Headysarum scoparium×Caragana korshinskii×Halloxylon ammondendron windbreak system proves to be the best, while pure Haloxyllon ammondendron forest(6m×9m) is simply the worst. 20 years after the establishment of sand-fixation forests, the intensity of crude sand particles (sand particles between 1.0～0.5mm in diameter) in the forest drops by 66.4%, while fine sand particles (less than 0.25mm) increase from 12.8%to 72.0%. Soil organic matter increases by 30.1%， total soil nitrogen by 48.3%, total soil phosphate by 76.3%, and total soil potassium by 58.0%. Both soil pH and total salt drop. There is a significant positive ecological effect of both sand-fixation forests and windbreaks on Heihe River valley soils in the past 20 years.