To investigate the seasonal variance of carbonic exchange in different grass carp ponds and explore the relationship between carbonic fluxes and environment factors of overlying water,three poly-culture systems,i.e.(1)GSB group:grass carp Ctenopharyngodon idellus,silver carp Hypophthalmictuthys molitrix and big head carp Aristichthys nobilis,(2)GSBL group:grass carp,silver carp,big head carp and Litopenaeus vannamei,(3)GSBC group:grass carp,silver carp,big head carp and carp Cyprinus carpio,were studied by simulation in the laboratory from April to September,2013.The changes of benthic fluxes of carbon across the sediment-water interface with time were studied,as well as the diurnal variation of carbon in the overlying water in August.The results showed that dissolved inorganic carbons(DIC)fluxes ranged from 0.65 mg/(m²·d)to 16.90 mg/(m²·d),while dissolved organic carbons(DOC)fluxes and particulate organic carbon(POC)fluxes ranged from 0.16 mg/(m²·d)to 3.49 mg/(m²·d),-2.29 mg/(m²·d)to 3.32 mg/(m²·d),respectively.Different carbon fluxes were all maximum in August for GSB and GSBC groups,but in July for GSBL group.During our experiments,the ex-fluxes of DIC and DOC were observed in every month.POC was up-taken by the sediments from April to June,but released from the sediments in other months.In the mid-to-late cultivation time,the benthic fluxes of DIC,DOC and POC in GSBL and GSBC groups were significantly higher than those in GSB group(P<0.05).The diurnal variation of carbons had obvious characters in August,with the content of DIC and DOC being maximum at 4:00 am.The content of POC in the GSBL got the maximum value at 4:00 am and the minimum value at 12:00 am,which was opposite to that of GSBC group.The results demonstrated a significantly negative correlation of carbon fluxes with DO and pH in overlying water,but a significantly positive correlation with overlying water temperature.