Pot sand culture of summer corn with Hoagland solution and soil culture of winter wheat with application of routine dosage of 0.15g N,0.05 g P and 0.10 g K per kg of soil were carried out in greenhouse of Nanjing Agricultural University. Leaves of corn and wheat were wiped or dipped with ¹⁵N-labelled 10 g/L urea, 10 g/L KH₂PO₄, 5.4 g/L KCl and their combinations from jointing stage of both crops to the silking of corn or heading stage of wheat. The root activities of both crops were rapidly declined after jointing stage, but this decline apparently delayed as foliar application of urea especially foliar feeding with N, P and K cooperated. Foliar feeding with macro-element fertilizers enhanced physiological activity of function leaves. Among the three elements for raising physiological indexes of function leaves urea-N was most efficient except small variation of total activity of RUBPase. Foliar application of N, P and K cooperated would be the measure for prolonging the life of leaves to the most limit. Statistical results showed that compared to foliar spray of water, urea+KCl and urea+KH₂PO₄ increased the yield of wheat significantly, while for corn only urea+KH₂PO₄ increased its ear and grain yields. Foliar application not only increased N, P and K content of plants, but also changed their distribution in organs and stimulated translocation of N to grain. Absolute protein contents of wheat and corn grains increased by 22 g/kg and 4.9 g/kg, respectively, due to foliar feeding during the middle and latter growing periods.