By using a full productive aged Lycium barbarum L. as the tested material, different amounts of N-P-K fertilizer were applied to study their effects on the chemical constituents, such as the contents of amino acid, betaine, and flavonoids. The results showed that: there were significant variations in different treatments. The contents of all 3 chemical constituents presented obvious rise and tended to be stable when the application of N-P-K fertilizer reached to a certain amount. The greater combination were N2P4K3, N3P3K3 and N3P4K2, while the combination which increased the effects of all 3 chemical constituents was N3P4K3. It could provide theoretical basis for the relationship between the contents of amino acid, betaine, and flavonoids and N-P-K fertilizer in Lycium.barbarum L. planting.