The organic loading of  sediments with shrimp  monoculture and  shrimp - tilapia   mixed - culture   was investi­ gated by the relative poiutant indexes ( Ap ) of tiiree multij^le contamination factors N, S and P in 18 experimental en­closures (the area： 36 m2) . These enclosures were divided into six groups, and each group has three parallels. All of the enclosures were put in 3 000 young shrimps ( Penaeusvannameii with the bodylength of (0.45 ±0.01 ) cm, in which ", I , $ , % , & and V enclosure groups were allowed to be stocked with 0, 4, 8, 12, 18 and 24 tilapias (OreochromismossambicusS with the body weight of (201 ±25) g respectively after one month. There was not water - exchange done  in     all of the   enclosures  during the experimental process.  The    experiment   period    was 70 d. The experi­mental results   showed as  follows ： 1)  The  contents  of N, P   and S increased   obviously     in   sediments  with   the   culture time lasting. However, the rate of increase in shrimp - tilapia mixed - culture enclosures was less than that in shrimp monoculture enclosures. 2) The values of Ipfollowed the order： "(10.78) > V(8.30) > I (7.68) >&(7.40) > $(6.09) >% (4.12), and  the value  of Ip of group III   was significant lower than  that  of  group "(P <0•    05).Therefore,     it can be   concluded that polyculture of shrimp at  the level of 8. 3 X  105  ind/hm2   and   tilapia  at     the   level   of 3 320   in^^hm2demonstrated  the best  ecological advantage. The   present study  provides a reference   in  shrimp  - tilapia carrying capacity management. [ Chinese Fishery Quality and Standards, 2015 , 5 (3 )：8 - 12 ]