In order to explore the influence of ricecrayfish ecosystems on weed in paddy fields,the characteristics of weed community changes and grass control effect in paddy fields with different years of ricecrayfish ecosystem were studied with ecological approaches to plant communities. This paper studied the differences of weed diversity between rice monoculture and ricecrayfish coculture in 1 year,2 years,4 years and 9 years. Field experiments were conducted to investigate the changes of weed species,weed quantity and weed coverage in fields and ridges after a complete 1year ricecrayfish coculture system. The results showed that the indexes of weed biodiversity in ricecrayfish coculture systems had a trend of decreasing first and then increasing with the increase of years. The Simpson index and Shannon diversity index under CK treatment had the highest weed dominance,which was significantly different from ricecrayfish treatments. The RC4 treatment had the lowest weed dominance. The evenness index of Pielou treated by RC9 has the highest evenness,which is not significantly different from that of CK but significantly different from that of other treatments. The total number of weeds in the sample plots with different years of ricecrayfish coculture system decreased first and then increased with the increase of the number of years,which were significantly lower than those treated with CK. The importance values (I values)of different weeds had different regularities with the increase of ricecrayfish cocultivation years. The I values of Leptochloa chinensis，Echinochhloa crausgalli，Paspalum paspaloides and Fimbristylis dichotoma decreased first and then increased with the increase of years. The I values of Mazus japonicus，Alternanthera philoxeroides，Eclipta prostrata and Monochoriav aginalis in ricecrayfish cocultivation paddy fields were smaller than those in rice monoculture paddy fields and decreased year by year. After 1 year ricecrayfish coculture farming，the number of weed species,weed individuals and weed coverage in the paddy field and the ridge were significantly reduced. The results showed that shortterm ricecrayfish coculture significantly improved the weed control effect. Longterm ricecrayfish coculture gradually formed a new weed community structure,and corresponding weed control measures need to be taken.