The experiment was carried out by sweet pepper cultivar ‘P13201’ in light growth incubator and nutrient solution to investigate the effects of pre-spraying different concentrations of 6-BA(5,10,20,50 μmol/L) on the growth and physiological and biochemical indexes of the sweet pepper seedlings under high temperature stress(40 ℃/30 ℃ day/night).The results showed that:(1)Growth index and chlorophyll content were significantly descended under high temperature stress,while plant height,stem diameter,shoot and root dry matter weight of sweet pepper treated with 10 μmol/L 6-BA concentration had no significant difference compared with the control check(CK),reduction of shoot and root fresh matter weight,contents of chlorophyll a,chlorophyll b and total chlorophyll of sweet pepper with this concentration were the smallest as well,among all the treatments.(2)Actual photochemical yield of PSⅡ(Yield),actual photochemical efficiency of PSⅡ(Ф_PSⅡ),optimal photochemical efficiency of PSⅡ in the dark(F_v/F_m) were significantly decreased under heat stress,while the non-photochemical fluorescence quenching(NPQ) showed a reverse trend.The extent of variation of four fluorescence parameters mentioned above in leaves of sweet pepper treated with 10 μmol/L 6-BA were the lowest among the all treatment groups,especially NPQ,displaying no significance with CK.(3)Affected by high temperature stress,the productivity of O^-·₂,activities of superoxide dismutase(SOD),ascorbic acid peroxidase(APX),peroxidase(POD) and malondialdehyde(MDA) content,relatively conductivity rate increased significantly.However,the productivity of O^-·₂.MDA content and relatively conductivity rate in leaves of sweet pepper treated with 10 μmol/L 6-BA were significantly smaller than those of T₀ treatment group(distilled water+high temperature).The activities of SOD,APX and POD revealed a remarkably increased tendency,namely,to rise by 50.5%,79.4% and 50.3% respectively.The study indicated that high temperature inhibited the growth of sweet pepper seedlings and made the above indexes in leaves changed a lot.There were dosage effect of 6-BA on the alleviation of high temperature in sweet pepper seedlings,10 μmol/L 6-BA,by means of enhancing activities of antioxidant enzymes,capturing and converting the light energy greatly,to maintain a normal growth,was the best relieving concentration to sweet pepper under heat stress.