Eco-substrates technology is known to improve water quality and promote growth of breeding objects in aquaculture.In this study,a 30-day experiment was conducted to investigate the effectiveness of the non-woven eco-substrates for maintaining good water quality and promoting growth in Ctenopharyngodon idella of high density.At the same time,the fish nonspecific immunity,fish intestinal microbial composition,water microbial composition and microbial composition of eco-substrates were analysed in this research.Microbial communities were analyzed by using the PCR-DGGE(PCR-denaturing gradient gel)technology.In treatment group,the non-woven eco-substrates were placed in farming ponds with the density 0.32 m²/m³,which was produced by AquaMats Company.By the end of the test,final fish weight,weight gain and growth rate in treatment group were significantly higher(P<0.05)than control,feed conversion ratio between the two groups was opposite(P<0.05).The serum AKP,ACP,SOD and LSZ activities for treatment group were significantly higher(P<0.05)than control,but iNos and tNOS were significantly lower(P<0.05)in treatment group.At the end of the test,the TSS in treatment group was significantly lower(P<0.05)than control.However,no differences were found between control and treatment group with respect to other water quality parameters.Cetobacterium somerae and Aeromonas veronii were the specific bacteria in control grass carp intestine,which didn't exist in intestine of treatment group.Bacterial community composition similarity between eco-substrates and treatment group water was much higher,and peaked at 63%.Cetobacterium somerae was specific dominant bacteria in control water.Aeromonas veronii existed only in water,and the distribution in control was higher than that in treatment group.Chloroflexi accounted for about 10% of the total bacteria for eco-substrates,but only 5% in water.The results demonstrated that non-woven eco-substrates could be considered a good tool for grass carp,mainly by promoting growth,reducing feed conversion ratio,improving nonspecific immunity and reducing TSS of water.The use of non-woven eco-substrates changed water bacterial community composition,reduced the number of opportunistic pathogens in water and intestine of grass carp.