Abstract: 【Objective】 To screen out the amount of nitrate nitrogen fertilizer suitable for the growth of the Coreopsis tinctoria seedlings. 【Method】 Coreopsis tinctoria was taken as the test material, nitrate nitrogen (Ca(NO₃)₂·4H₂O) as test fertilizer to carry out pot experiments. According to the completely random block design, six levels of nitrate nitrogen treatment were set up. The application rate of nitrate nitrogen per pot was 0.10g, 0.15, 0.20, 0.25, 0.30 g/kg. The effects of different nitrate nitrogen treatments on the growth and metabolites of Coreopsis tinctoria seedlings were studied. 【Results】Different nitrate treatments had certain effects on Coreopsis tinctoria seedling growth and metabolites. When the nitrate nitrogen application rate was 0.25 g/kg, the plant height of the Coreopsis tinctoria seedlings was the best, which was 7.26 cm; When the application rate of nitrate nitrogen was 0.3 g/kg, the fresh weight, stem diameter, number of branches, SPAD value and soluble protein content of Coreopsis tinctoria seedlings were the best. The SPAD value and soluble protein content were 48.92 and 8.86 mg/g. Nitrate nitrogen could promote the soluble sugar of Coreopsis tinctoria seedlings. When the nitrate nitrogen application rate was 0.25 g/kg, the soluble sugar content was the highest, which was 32.63%. Root-shoot ratio, root length, chlorogenic acid, total flavonoids in leaves and total flavonoids in roots were highest in control Coreopsis tinctoria seedlings. The total flavornoids in leaves and roots were 90.70 and 34.77 mg/g. The chlorogenic acid content in the leaves was 10.85 mg/g. When the nitrate nitrogen application rate was 0.3 g/kg, the PAL activity in the Coreopsis tinctoria seedlings was the lowest, which was 10.76% lower than that of the control. 【Conclusion】 The results of this test showed that little or no application of nitrate nitrogen was beneficial to improve the PAL activity of leaves of the Coreopsis tinctoria seedlings and increased total flavonoids and chlorogenic acid content in roots and leaves of seedlings, however, the application of less or no nitrate nitrogen significantly inhibited the growth and dry matter accumulation of the Coreopsis tinctoria seedlings. Therefore, considering the growth status of the Coreopsis tinctoria seedlings, the nitrate nitrogen application rate is preferably 0.25 to 0.3 g/kg of nutrient soil.