Abstract: Gas exchange and chlorophyll fluorescence quenching kinetics were investigated to explore the effect of low phosphorus stress on photosynthesis, chlorophyll fluorescence characterisitics and excitation energy distribution in rapeseed during different developing period .The results showed that Pn was significantly decreased in stem elongation and flowering stage,while Fm 、Fv and Fv／Fm remained unchanged during three developing periods ,indicating that PSⅡ primary reaction centres were not affected by low phosphorus stress.However, ФPSⅡ、ETR、qP were significantly decreased and NPQ wes significantly increased under the low phosphorus stress. In the aspect of excitation energy distribution,both D and Ex increased while P declined significantly. It suggested that the pathway of electron transport through PSⅡ was blocked,In this case,the plant of rapeseed had triggered exicitation energy dissipation to confess the low phosphorus stress.