Abstract: Taking C2 and C5 tomato germplasm with different resistance as experimental materials, pot experiments were carried out and three saline-alkali soil treatments with different stress degrees were set up.Compared with non-saline-alkali stressed soil, the effects of different saline-alkali stress degrees on photosynthetic gas exchange parameters of two tomato varieties, as well as the rapid chlorophyll fluorescence kinetic curve and parameters of leaves were studied, in order to provide reference for further comprehensive analysis of tomato salt-alkali tolerance mechanism and salt-alkali resistance breeding.The results showed that saline-alkali stress reduced the net photosynthetic rate and affected the parameters of light and gas exchange by inhibiting the synthesis of chlorophyll in tomato.Saline-alkali stress reduced the maximum photochemical efficiency, actual photochemical efficiency, photosynthetic electron transfer rate and photochemical quenching coefficient of the two tomato varieties.At the same time, saline-alkali stress also changed the shape of OJIP curve of two tomato varieties.To sum up, saline-alkali stress would reduce the activity, electron transfer efficiency and photochemical efficiency of PSⅡ reaction center of C2 and C5 varieties, harm OEC and PSⅡ receptor side, reduce chlorophyll content, and thus reduce the net photosynthetic rate.In case of saline-alkalitress, C2 variety had higher PSⅡ reaction center activity and electron transfer rate than C5 variety, improved the net photosynthetic rate, and reduced the damage caused by saline-alkali stress by dissipating excess light energy, so the growth inhibition degree was significantly lower than C5 variety.