Abstract: The changes of chlorophyll content, photosynthetic parameters and chlorophyll fluorescence parameters of flag leaves in three hybrid rice combinations during grain filling were investigated. The results showed that Pn, Tr, Ci, Gs, Fv/Fm, ETR in leaves and Yield of different hybrid rice combinations during grain filling showed a wavelike decrease change with the development of seeds. The changes of these parameters were also significantly different. The Pn of Feiyou188 and B2You768 were much higher than Gangyou725 at the early stage of grain filling. Then, the Tr, Gs, Ci and Fv/Fm of Feiyou188 and B2You768 decreased gradually at the medium stage of grain filling, while these parameters of Gangyou725 were volatile during this period. The effective spike number, 1000-grain weight, grain yield of Feiyou188 and B2You768 were much higher than Gangyou725, showed better qualities.