With two-line hybrid r ice Yangliangyou 6 and L iangyoupeijiu and three- line hy brid r ice Shanyou 63 as materials, the relationships of source, sink and flow with grain filling w er e studied. T he seed- setting rate, grain filling deg ree and gr ain yield of Yangliangyou 6 and Shanyou 63 were sig nificantly higher than those of L iangyoupeijiu. T he export per centage and transformation percentage of the matter in culms and sheaths of Yang liang you 6 and Shanyou 63 w er e sig nificantly higher than those of Liangyoupeijiu. Activities of sucro se synthase, adenosine diphosphoglucose pyrophosphorylase, star ch sy nthase and starch branching enzyme in grains were higher in Yangliangyou 6 and Shanyou 63 than in L iangyoupeijiu, and were very significantly cor related w ith max imum grain filling rate, mean g rain filling rate, g rain filling degree and grain w eight. T he spikelet number , grain yield and total sink load per area of vascular bundle and phloem of Yangliangyou 6 and Shany ou 63 were significantly sma-l ler than those o f L iangyoupeijiu, and the g reater the load, the lower the seed-setting rate and the poorer the g rain filling. T he transportation rate per ar ea phloem of Yangliangyou 6 was gr eater than that of L iangyoupeijiu o r Shanyou 63. T he results sugg ested that Yang liang you 6 possesses strong sour ce, g reat sink activ ity and efficient flow, which lay a physio logical basis for its high seed- setting rate and good grain filling.