In order to evaluate the cold tolerance and photosynthetic characteristics in different sugarcane genotypes,and understand the correlations between changes of photosynthetic characteristics and cold tolerance,7 newly bred sugarcane lines from Sugarcane Research Institute,Guangxi Academy of Agricultural Sciences,and 2 commercial main cultivars were used as plant materials in present study.The plants were grown at 4oC chamber for 0,7,15,25,31 and 38 days as low temperature treatment,while the control was at room temperature(about 25℃).Chilling injury index,chlorophyll content and photosynthetic parameters under low temperature stress were determined.The results showed that chilling injury index increased with the rise of low temperature treatment days,while changes of chilling injury in different sugarcane genotypes were different.Chlorophyll content decreased as the days of low temperature treatment increased.Under cold stress,net photosynthetic rate(Pn)and stomatal conductance(Gs)decreased sharply; Pn and Gs showed significant differences between control and low-temperature treatment.Maximum efficiency of light energy conversion(Fv/Fm),PSII actual quantum efficiency(ΦPS_),reaction center of excitation energy capture(Fv′/Fm′),photochemical quenching coefficient(qP)and electron transfer rate(ETR)significantly decreased under cold stress,but initial fluorescence(Fo),Steady state fluorescence(Fs)and non photochemical quenching coefficient(qNP)increased.Different genotypes showed differences in photosynthetic capacity and chlorophyll fluorescence.Both chlorophyll content and photosynthetic parameters had positive correlations with chilling injury indexes,especially Fv/Fm,Fv′/Fm′ and ΦPS□ showed highly positive correlation coefficients with the chilling injury indexes,so Fv/Fm,Fv′/Fm′,ΦPS_ could be used as the indexes of cold tolerance in sugarcane.