Abstract: [Objective] This study aims to investigate the differences of leaf chlorophyll fluorescence characteristic parameters between different genotypes of cotton under different temperatures and to provide a theoretical basis to screen suitable indexes for evaluating high temperature-tolerance of cotton varieties.[Method]Chlorophyll fluorescence characteristic parameters in leaves of cotton seedlings of four different genotypes(13-1 strain,Xinhai 24,13-1×Xinhai 24 hybrid,13-1×Xinhai 14 hybrid)were determined by rapid fluorescence detector(Handy PEA-100)under 25℃,30℃,35℃,40℃,45℃ and 48℃ respectively.[Result]The performance index of PIABS,maximum photochemical Fv/Fm and electron transfer yield φEo increased at first and decreased subsequently as the temperature increased,the heat dissipation DIO/CSO,initial fluorescence FO was on the contrary.PIABS performance index between the four different genotypes of strains was extremely significant at 40℃,and it could more accurately reflect photosynthetic status than Fv/Fm.[Conclusion]Using the method of subordinate function to analyze the four different genotypes,it is found that 13-1×Xinhai 24(hybrid)has the highest subordinate function value,and we believe that it belongs to heat resistant strains.