Abstract:To explore the salttolerance and its physiological mechanism of daylily, with the normal nutrient solution as control, the experiment studied the effects of NaCl stress on the growth, lipid peroxidation and organic osmotic substances contents of Datong daylily in sand culture by irrigating the different concentrations (50, 100, 150, 200, 250 mmol·L-1) of NaCl solution and measuring the growth and physiological indicators at 5, 10, 15, 20, 25 d after treatment. The results showed that: (1) with the increase of NaCl concentration, the root length and root fresh weight were increased and then decreased, the other growth indexes were decreased significantly, and the aboveground water content was relatively stable, and root water content was increased obviously. (2) The contents of chlorophyll a, chlorophyll b and carotenoid in leaves of daylily were decreased obviously with the increase of NaCl concentration. (3) With the rise of NaCl concentration, the MDA content and POD activity were increased drastically, the AsA content was increased within 20 d after treatment, and showed the trend of “increasedecrease” and reached the maximum at 150 mmol·L-1 at the 25th day. The SOD activity showed the law of “increasedecrease” and reached the peak value at 200 mmol·L-1 within 10 d after treatment, and was increased significantly with the rise of NaCl concentration after 15 d. (4) With the increase of NaCl concentration, the proline content was increased drastically, the soluble sugar content was decreased obviously, the soluble protein content was increased with the rise of NaCl concentration in short period, and showed the trend of “increasedecrease” and reached the maximum at 150 mmol·L-1 NaCl after 15 d. The research illustrated that the greater the NaCl concentration, the greater the inhibition degree to the photosynthetic pigment synthesis and the peroxidation damage to the daylily plant. The abilities of antioxidance and osmotic adjustment of plant under stress were increased obviously, but the change could not eliminate the adverse effect by NaCl stress. It made that the growth of daylily plant was reduced significantly. The salttolerance of daylily was very strong, the plant can survive under 250 mmol·L-1 NaCl stress.