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The mechanism of high yield of winter wheat in the field at late growth period was investigated by measuring the photosynthetic characteristics of photosystem Ⅱ (PSII) and xanthophylls cycle,which could provide physiological reference for breeding. Weimai 8 (W8),a super high yield cultivar,and Lumai 14 (L14),a control cultivar were object. The photosynthetic rate (Pn),parameters of chlorophyll fluorescence and chlorophyll content were measured. The Pn,maximum photochemical efficiency of PSII (Fv/Fm),quantum yield of PSII electron transport (φPSII),efficiency of excitation energy capture by open PSII reaction centers (Fv'/Fm'),and photochemical quenching coefficient (qP) were higher in Weimai 8 compared to that in Lumai 14,a commercial high yield cultivar. Furthermore,Weimai 8 showed a lower non-photochemical quenching coefficient and a lower de-epoxidized ratio of the xanthophyll cycle pigments than of Lumai 14 at late growth period. At mature stage,chlorophyll content of different leaves decreased both in Weimai 8 and Lumai 14.Chlorophyll content in flag,second and third leaf from the top of plant decreased more in Lumai 14 than in Weimai 8. These results suggested that Weimai 8 had more antenna pigments to absorb light energy,and had higher photosynthetic capability and photochemical efficiency of PSII. The yield of Weimai 8 was also higher than that of Lumai 14.