‘Hanxiao’ was selected as material to study the effects of 0.5 mmol/L exogenous spermidine(Spd) on the growth and quality of pakchio seedlings under 80 mmol/L calcium nitrate stress by hydroponic culture.The results showed that:(1)The stress of 80 mmol/L Ca(NO₃)₂ significantly reduced plant growth,plant height,root length,leaf area,root volume,fresh and dry weight.Spraying 0.5 mmol/L Spd on leaf significantly promoted the growth of seedlings.(2)The stress of 80 mmol/L Ca(NO₃)₂ significantly reduced the contcents of photosynthetic pigments.Compared with CK treatment,chlorophyll content in seedlings declined 54.72% with Ca(NO₃)₂ treatment.Spraying 0.5 mmol/L Spd on leaf significantly promoted the contents of photosynthetic pigments in seedlings.Compared with Ca(NO₃)₂ treatment,carotenoid contcent in seedlings increased 53.33% with NS treatment[Ca(NO₃)₂+Spd].(3)The stress of 80 mmol/L Ca(NO₃)₂ significantly reduced photosynthesis.Compared with CK treatment,P_n of seedlings declined 34.45% with Ca(NO₃)₂ treatment.Spraying 0.5 mmol/L Spd on leaf significantly promoted P_n of seedlings.Compared with Ca(NO₃)₂ treatment,P_n of seedlings increased 28.11% with NS treatment.(4)The stress of 80 mmol/L Ca(NO₃)₂ significantly reduced quality.Compared with CK treatment,the contents of vitamin C,soluble sugar and soluble protein of seedlings significantly declined,nitrate and organic acid significantly increased with Ca(NO₃)₂ treatment.Spraying 0.5 mmol/L Spd on leaf significantly promoted seedlings above-mentioned nutritive index.These results indicated that exogenous Spd significantly promoted the growth,photosynthesis and improved the quality of pakchoi seedlings under calcium nitrate stress.