The effects of alkali solution 〔n（Na₂CO₃）∶n（NaHCO₃）=1∶1〕 treatments with different concentrations of 0 （CK）， 20， 60， 100， 140， and 180 mmol·L^-1 on photosynthetic characteristics and physiology of leaves of Taxodium ‘Zhongshanshan 406’ seedlings were studied by pot method. The results show that with enhancing of alkali concentration， chlorophyll content and stomatal conductance of leaves of T. ‘Zhongshanshan 406’ seedlings first decrease and then tend to be stable， net photosynthetic rate， transpiration rate， and intercellular CO₂ concentration generally decrease gradually， water use efficiency increases gradually， soluble sugar and soluble protein contents increase in fluctuation， and superoxide dismutase activity first increases and then decreases. In general， compared with CK group， chlorophyll content， net photosynthetic rate， transpiration rate， stomatal conductance， and intercellular CO₂ concentration decrease significantly， and water use efficiency， soluble sugar and soluble protein contents， and superoxide dismutase activity increase significantly. In summary， alkali treatment can inhibit the photosynthesis of leaves of T. ‘Zhongshanshan 406’ seedlings to a certain extent， and under 20-100 mmol·L^-1 alkali treatment， T. ‘Zhongshanshan 406’ can accumulate soluble sugar and soluble protein and improve superoxide dismutase activity to adapt to alkali stress environment.