Abstract: By the techniques of PEG, one-year-old seedlings of 8 Catalpa bungei varieties or types grew in phytotron. The effects of different levels of water stress on its photosynthetic characteristics were studied. A completely random experiment was designed with 4 treatments and 3 replicates. The results showed that the chlorophyll fluorescence parameters of 8 varieties of catalpa bungei, e.g., the net photosynthesis rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), intercellular CO2 concentration (Ci), Fv/Fm and Fv’/Fm’, decreased due to water stress. The decreases of these parameters were smaller in 4% water stress while they were greater in 8% and 12% water stress. The decreases of Pn and Ci were mainly caused by the decrease of Gs for 4 varieties of Zhou-2, Guang-ye, Zi-shu and Nan-yang. For variety of Qiu-shu, Yuan-chang, ’Yu-1’ and Jin-shi, the decreases of Pn and Ci were not caused by stomatal conductance, but they are due to the decrease of photosynthetic capacity of mesophyll cells. It was seen that Nan-yang, Guang-ye, Zhou-2 and Jin-si was more tolerant to water stress than ’Yu-1’, Qiu-shu, Zi-shu and Yuan-chang.