Abstract: In order to improve sunflower＇s yield and fertilizer utilization, the oil-sunflower variety named S31 was choose to study , the regularity of leaf area index variation, dry matter accumulation and the effect of NPK fertilizer were analyzed by the methods field experiments and indoor chemical analysis. The results showed that： the leaf area index changed as a single peak cure during the whole growth period, and the organ and the plant DM accumulation process of sunflower showed ＂S＂ curve. In the OPT treatment, the DM accumulation reached to the maximum. Balanced fertilization increased the sunflower yield with the fertilizer effect order N 〉 P 〉 K and the N nutrient is the most important factor for the sunflower yield.