In this study, Tiefeng 31 seedling leaves were sprayed with 1500 mg•L-1 KHCO3 and NaHCO3, respectively, and determined the photosynthetic rate, soluble sugar, photosynthetic pigment and other physiological indexes to explore the effect of K +, Na+ and HCO3ˉ on soybean seedlings photosynthesis. The results showed that: compared with water spraying control , K +, Na+ and HCO3ˉ improved soybean seedlings photosynthetic rate, the content of soluble sugar, chlorophyll a,chlorophyll b,and the ratio of chlorophyll b in total chlorophyll; promoted soybean seedlings photosynthesis by providing more assimilatory power to dark reactions carbon fixation; and enhanced the activities of ATP enzyme, photophosphorylation, and PEPC. In addition, HCO3- played a more important role in promoting chlorophyll b synthesis and improving photosynthetic rate. NaHCO3 significantly increased the content of Rubisco. For other physiological indexes but the content of Rubisco, the promotion of K + is more than Na+.