Abstract: In order to investigate the changes of photosynthetic characteristics during the discoloration period of the P.quinquefolia,and elucidate the optimal light environment for its growth and development.The leaves of P.quinquefolia were taken as the material to determine the four stages of the discoloration periodCⅠ（dark green leaf）-CⅡ（red green leaf）-CⅢ（dark red leaf）-CⅣ（bright red leaf）leaf color parameters（Lab model）,pigment content and photosynthetic characteristics are related index.Then carry out ANOVA analysis of variance and correlation analysis.The results showed that the leaf color parameter a^*value was significantly increased from-2.95to 9.75during the discoloration period.The chlorophyll content decreased while the anthocyanin content increased,and the chlorophyll content and anthocyanin content were 3.19%and 26.19times that of the CIV.stage,respectively.The leaf color parameter a^*value was extremely significantly negatively correlated with chlorophyll content,and extremely significantly positively correlated with anthocyanin.The maximum net photosynthetic rate (Pn_max),stomatal conductance （Gs）,water use efficiency （WUE）,and transpiration rate（Tr）of P.quinquefoliaduring the discoloration period changes with the leaves red continued to decline,and both were significantly positively correlated with chlorophyll content.The light saturation point was significantly reduced to 92.4μmol·m^-2s^-1in the CIV stage.And the light compensation point decreases significantly in the CⅡstage,which was only 20.14%of the CⅠstage;The apparent quantum efficiency decreased significantly to 62.50%and 8.33%of CⅠcompare with the CⅢand CⅣstages,respectively.The dark breathing rate does not change significantly.Research shows that the chlorophyll decreases and the anthocyanin increases are the main reasons that cause the leaf color to turn red.The decrease in chlorophyll content caused the decline of photosynthetic capacity of P.quinquefolia.There was no significant difference in the ability of leaves to absorb bright light before turning completely red,but the efficiency of using low light and the ability to use water were reduced.