In order to investigate the physiological regulation mechanism of exogenous chitosan on vegetable soybean photosynthesis,we studied the effects of exogenous chitosan on photosynthetic and chlorophyll fluorescence parameters in seedling leaves of two vegetable soybean ［Glycine max (L.) Merr.］ cultivars with different salt tolerance under NaCl stress by adopting vermiculite culture.The results showed:(1)exogenous chitosan alleviated the decline of net photosynthetic rate (P_n) of salt-sensitive cultivar LX markedly at the 6th,9th and 12th days of salinity by inducing non stomatal factors,but this effect disappeared after 15 days of salt stress.For salt-tolerant cultivar LL,chitosan reduced the decline of P_n significantly at the 3rd and 6th days of salinity by inducing stomatal factors and non stomatal factors simultaneously,and reduced that of the 9th,12th and 15th days of salt treatment mainly by inducing non stomatal factors,and its growth of P_n compare with NaCl treatment were higher than that of LX.(2)Exogenous chitosan prevented the decline of non photochemical quenching coefficient (NPQ) of LX after 12 days of salinity,and prevented the decline of NPQ and markedly alleviated the decline of photochemical quenching coefficient (q_P) and actual photochemical efficiency (Ф_PSⅡ) of LL after 15 days of salinity.(3)Under no NaCl condition,chitosan increased the P_n of two vegetable soybean cultivars significantly by inducing stomatal factors and non stomatal factors such as stomatal conductance (G_s),q_P and Ф_PSⅡ at the early stage of spraying chitosan,but these effects disappeared at middle and later stage.All the results suggest that:vegetable soybean has potential resistance.The effects of exogenous chitosan on vegetable soybean under NaCl stress differ from those of no NaCl condition.Chitosan can only induce potential salt resistance of vegetable soybean when it is injured by salt stress.However,the induction route,induction timeline and induction effect of chitosan on vegetable soybean were different because of different salt tolerance of vegetable soybean.The salt tolerant cultivar LL has strong,durable and multiple potential resistance ability,which may play an important role in maintaining relatively higher P_n induced by chitosan.