Abstract: A solution cultivation experiment with Pinus koraiensis seedlings was conducted to study the effect of different NH+4/NO-3 ratio on nitrogen absorption，nitrogen assimilation enzyme and growth. The results showed that more nitrogen was absorbed by the seedlings in high NH+4/NO-3 ratio solution, whose total biomass was more than the others. Nitrate reductase (NR) activity was higher in the roots than the leaves, NO-3 promoted NR activity, which responsed to increased NO-3 availability of the solution. Glutamine synthetase (GS) activity and glutamate dehydrogenase (GDH) activity was improved by the induction of exogenous NH+4. GS activity was higher in the leaves than the roots, and which was higher in the seedlings of high NH+4/NO-3 ratio solution. GDH activity of the roots and the leaves was high, and which was higher in the seedlings of high NH+4/NO-3 ratio solution.