Abstract: It was found that the mutant of Anabaena siarnensis which was obtained from monoclonal culture of spaceflight Anabaena is of higher growth rate and photosynthetic efficiency than the ground control.To explain the differences between the mutant and the control, The composition of pigments, chlorophyll fluorescence and the ratio of PSII/PSI was investigated.Results showed that the ratio of PC/Chl in mutant was lower than that in the control, but the chlorophyll fluorescence and the ratio of PSII/PSI were higher than those in the control.The results suggested that the higher efficiency in energy harvesting and in energy utilization of the mutant than those of the control is due to the photosynthetic characteristic discrepancy.