Abstract: Potassium treatment did not obviously increase chlorophyll content per unit leaf area, but increased the net photosynthetic rate, decreased the rate of respiration, the ratio of photorespiratory rate/net photosynthetic rate, light compensation point and CO2 compensation point. The results also showed that the stimulating photosynthetic function of potassium was affected by the applicate levels of nitrogen and phosphorus.Potassium treatment significantly increased potassium content and carbohydrate accumulation in leaves and decreased relative abscission rate of fruits. The contents of both potassium and starch in leaves rapidly declined after full bloom. It was suggested that the first wave of fruit-drop be closely related with lack of potassium of trees after full bloom and a decline of potassium concentration of fruits, while carbohydrate deficency be a main factor in the second wave.