Abstract: A controlled hydroponic experiment was conducted utilizing seedlings from various half-sibling families of Cunninghamia lanceolata as research subjects. Following treatments involving regular phosphorus supply and low phosphorus stress for 15 days, the seedlings were further cultivated for an additional 15 days under 4 levels of nitrogen supply (0.5×, 1×, 1.5×, and 2×) across both phosphorus conditions. The changes in root morphology, root secretion, protective enzyme activity, nitrogen metabolism related enzyme activity, and nitrogen and phosphorus metabolism related gene expression of C. lanceolata seedlings under normal phosphorus supply and low phosphorus stress were analyzed. This study aims to elucidate the adaptive mechanisms of C. lanceolata seedling roots in response to varying intensities of nitrate nitrogen application under the specified phosphorus conditions. It was found that the root morphological response of C. lanceolata family 10 was the most sensitive, and the high intensity nitrate treatment under low phosphorus stress significantly promoted root proliferation and lateral root growth. The addition of nitrate nitrogen could significantly alleviate the decrease of phosphorus content in roots of family 10 due to phosphorus deficiency stress and significantly increase the secretion of acid phosphatase and organic acids in roots. The activities of superoxide dismutase, catalase and peroxidase, and the content of malondialdehyde in roots decreased significantly. In addition, nitrate nitrogen addition could not effectively alleviate the weakening of nitrogen metabolism activity caused by low phosphorus stress. Under low phosphorus stress, nitrate reductase(NR) activity and nitrite reductase(NiR) activity decreased significantly in family 10, while NR and NiR activities in roots of nitrate nitrogen treatment were still lower than those of normal phosphorus treatment. The results of quantitative PCR analysis showed that the addition of nitrate nitrogen under normal phosphorus supply could significantly down-regulate the expression of ClNRT1.1, ClNIR1 and ClCPR2 to reduce nitrogen uptake and metabolism, while under low phosphorus stress, nitrate nitrogen addition could significantly up-regulate the expression of ClNIR1 and ClCPR2 to increase the ability of nitrate nitrogen reduction, thus improving the ability to adapt to high nitrogen and low phosphorus environment.