The effects of nitric oxide on non-structural carbohydrate metabolism of Medicago sativa seedlings leaves and roots under drought stress by 10% PEG were investigated. Solutions with:(i) osmotic potentials obtained using polyethylene-glycol-6000 (PEG-6000); (ii) a nitric oxide donor sodium nirorpusside (SNP); (iii) an NO scavenger (carboxy-PTIO, cPTIO); were sprayed onto the leaves of alfalfa seedlings in pot experiment at different combinations. The results showed that exogenous nitric oxide promoted the starch decomposition of leaves, the accumulation of starch in roots and increased the content of soluble sugar (sucrose, fructose and glucose) in leaves and roots in Medicago sativa seedlings under drought stress, which decreased the osmotic potential, promoted cell water absorption and alleviated damage caused by drought. Furthermore, under drought stress exogenous nitric oxide can increase the activity of sucrose synthetase (SS), acid invertase (AI), neatral invertase (NI), reduce the activity of Sucrose phosphate synthase(SPS) in leaves and can increase the activity of SS, SPS, invertase in roots, so that make the synthesis and decomposition of sucrose at a high level of dynamic balance. It enhances the drought resistance of alfalfa. The metabolism of NSC and related enzymes were inhibited by NO scavenger cPTIO. Therefore, nitric oxide played an important role in the drought resistance of Medicago sativa. It can regulate the metabolic of NSC response to drought stress and alleviate the adverse effects caused by drought stress.