Abstract: Changing characteristics of weed community, weed-controlling effect of large-scale rice-duck eco-farming (SF), conventional rice-duck eco-farming (CF) compared to mono-cropping rice (CK) were analyzed in order to explore the dynamics of weed communities in large-scale rice-duck eco-farming paddy fields. The study shows that weed density in paddy fields significantly decreases with more than 94% grass-controlling effect under SF compared with CK. Before rice booting stage, weeds compose mainly of Alopecurus pratensis, Echinochhloa crausgalli,Cynodon dactylon, Alternanthera philoxeroides, Mouochoria vaginalis,Murdannia triquetra and Eclipta prostrata in SF. During heading to ripe stage, weeds are mainly A. philoxeroides, E. crausgalli, C. dactylon, M. triquetra. At tillering, species richness, Simpon index and Shannon-Wiener index are higher while Pielou index is lower in SF than in CK. From booting to ripening, weed species richness, Simpon index and Shannon-Wiener index are lower while Pielou index is significantly higher in SF than in CK. In the entire rice growth period, weed density, weed fresh weight and species diversity are not significantly different between SF and CF, but species diversity is higher in SF than in CF. SF changes the structure of weed community and decreases weed species diversity, effectively limiting weed infestation in paddy fields.