Abstract: The pot experiment was conducted to determine the effects of the different concentrations [0(The control), 0.02, 0.10, 0.50, 2.50 mmol/L] of salicylic acid on the growth, the physiology characteristics and photosynthetic characteristics of Melilotoides ruthenica in branching stage under normal irrigation (80% field capacity), mild water stress (60% field capacity), moderate water stress (40% field capacity)and severe water stress (20% field capacity) in order to understand the effects of salicylic acid on drought tolerance of M. ruthenica in branching stage. The results showed that under mild and moderate water stress, treatment with 0.1 mmol/L salicylic acid significantly increased leaf relative water content, chlorophyll content, soluble protein content, the activities of superoxide dismutase (SOD), peroxidase (POD) and catlase (CAT), photosynthetic rate (Pn) and stomatal conductance (Gs) compared with the control, but stomatal limitation value (Ls) were significantly decreased; Under severe water stress, treatment with 0.5 mmol/L salicylic acid significantly increased plant height, primary shoot number, leaf area, leaf relative water content, chlorophyll content, free proline content, soluble protein content, the activities of SOD, POD and CAT, Pn, Gs and water use efficiency (WUE) compared with the control, but electrolyte leakage, malondialdehyde (MDA) content and Ls were significantly decreased. The results suggested that salicylic acid with the appropriate concentrations could increase the drought resistance of M. ruthenica and improve its growth in branching stage under water stress.