According to the principle of nutrient balance, the nutrient movement in different organs of blacklocust about the leaching of leaves has been analysed. The flux and cycling rates of every nutrient participating in internal and external nutrient cyclings have aslo been calculated and the results show that the nutrients of N、P、K、Mg and S backflow (from leaves and fruits to other organs) in different extents before the leaching of leaves and the backflowing rates are 63．94％，61．83％，76．39％，18．33％ and 69．60％. respectively except that Ca flows from other organs to leaves and fruits and makes their Ca content 2 times as before. Amonge these nutrients, the gross cycle rate of K is 59.81%, as the greatest of all, and the others are 26.17%～3719%. N、P、K participate in internal cycles mainly and the intercycle rates are 22.86%, 16.18% and 51.51% respectively, but their extercycle rates are 8.35%～9．99％. Ca、Mg and S praticipate in both intercycle and extercycle with the similar cycle rates nearly as 15.10%～2183%. The results aslo show that blacklocust absorbs K、 Mg from soil and gets rid of S with raindrop or secretion in little amout about the leaching of leaves.