Abstract: Six early-hybrid rice combinations were studied. They have been found, their seed-set rates were significantly different.These combinations were testcrossed with MS line V41A, and their F1 were observed and analysed about their fertile characters separately. The results indicated that fertility of hybrid rice mainly decided on strong one of two pairs of restorer genes (R2) and their "Synergism" in hybrid plant.For instance,the seed-set rates of Weiyou 35 and Weiyou 057 were higher, because their restoring abilities of the R2 were strong and the synergistic effects of two genes were high. In Weiyou 6 the fertility restoring ability of the R2 was low, but the "Synergism" of two restoring genes was satisfactory,therefore, its seed-set rate was stable. In Weiyou 437 the seed-set rate restoring effect of R2 was weak, and its seed-set rate was generally lowest. According to the correlation coefficient between the normal pollen rate and the seed-set rate, the testcrossing plots of Shanyouphi 1 and Weiyou 3533 were rather small, therefore, their seed-set rates were unstable. To sum up,in breeding strong restorer line we must emphasize the selection of strong restorer gene R2 and good "Synergism" between two restoring genes.