Photosynthesis is one of the plant relatively sensitive physiological metabolism reaction to
salt stress．This experiment took 2 cucumber varieties‘ Zhongnongda No.22’ and‘ Deltastar’ with different
sensitiveness to salt stress as material to study photosynthetic responses to salt stress． The results showed that the
photosynthetic pigment（chlorophyll and carotenoid）contents，net photosynthetic rate，dark respiration rate and
transpiration rate of cucumber seedlings decreased significantly under salt stress．The number of thylakoid lamella
of chloroplast was reduced greatly and starch grains became fewer and smaller when cucumber seedling treated
with salt stress．With the process of salt stress，the expression levels of rbcL，encoding the large subunits of
Rubisco（ ribulose-1，5-bishosphate arboxylase/oxygenase）and Csppc2，encoding PEPC（phosphoenolpyruvate
carboxylase） increased first then decreased，while the enzyme activity of Rubisco and PEPC declined
remarkably．Compared with‘ Zhongnongda No.22’，‘Deltastar’ had better tolerance to salt stress．