Abstract: Plants grown on the both banks of tidal rivers or river channels with the water level fluctuating seasonally must possess the characteristic of tolerance against flooding. In this study, a flooding experiment was conducted to investigate the variations of survival rate, chlorophyll content, root vitality and root to shoot ratio in order to explore the responses to flooding stress and explain the physiological mechanisms for the flooding tolerance in Indigofera spicata. Six flooding treatments were carried out, including water levels at 5, 10 and 20 cm above soil surface and at 0, 15 and 40 cm above plant top. This work could provide the theory basis for the feasibility of I. spicata using for both banks of tidal rivers or river channels with the water level fluctuating seasonally. The results showed that: 1) I. spicata had a survival rate of 100% after 21 d flooding. Before I. spicata was flooded, the chlorophyll content was 1.94 mg/g. After 3 days of flooding, the chlorophyll contents decreased to 63.2% and 83.9% of the initial value. But the chlorophyll contents were 1.21-1.69 mg/g after 21 days of flooding. This implied that chlorophyll content significantly decreased under flooding stress (P<0.05) but it could maintain a certain level for a long time. 2) Root vitality of underground root significantly decreased with the increasing of flooding time. The initial value was 256.26 μg TTC/(g·h), but the values had decreased to 23.43-71.96 μg TTC/(g·h) after 21 days of flooding. However, adventitious root with stronger root vitality rapidly produced in the flooded stems under semi-submerging conditions. The root vitalities of adventitious root were 123.74-234.31 μg TTC/(g·h) on days 21 of semi-submerging. 3) Shoot biomass significantly decreased and root to shoot ratio gradually increased 6.9%-142.5% with the increasing of flooding duration. This indicates that I. spicata has a strong flooding tolerance, which may make it be able to be applied in river channels of water level changes.