Abstract: The photosynthetic and fluorescence characteristics of “Hai7124” (Gossypium barbadense), “Jinhuazhongmian” (G. arboreum), “Hongxinmian” (G. herbaceum) and “Su12” (G. hirsutum) were analyzed in this paper. The results show that total chlorophyll content, leaf mass per area, Pn, PSⅡ photochemical efficiency (Fv/Fm) and photochemical quenching (q^P) of the cotton cultivars are the following order: “Hai7124” > “Su12” > “Jinhuazhongmian” > “Hongxinmian”; indicating that “Hai7124” has higher photosynthetic efficiency. Further investigation shows that diurnal variation curves of Pn for “Hai7124”, “Jinhuazhongmian” and “Su12” have two peaks that occur at 12:00 and 16:00, though Pn for “Hongxinmian” varies and has a uni-peak curve that occurs between 12:00 ～ 14:00. This is consistent with diurnal variations in stomatal conductance (Cs). Photoinhibition of photosynthesis at noon is related with decreasing Cs and PSⅡ photochemical efficiency.