Multiple sampling cores of pond sediments for a intensive, poly-culture fishpond were bacteriologically and chemically analysed. The results indi-cated that species and number distribution of bacteria involved in N-cycle and theN-containing substances in pond sediments varied vertically with depth. Thebacteria activities enrolled in N-cycle were mainly subject to the interactions ofbacterial number, dominating species and its type of metabolism, metabolic sub- strates, oxygen in sediments and other environmental factors. Growth of obligateaerobes is suggested to be the major indicator for estimating the activity of pondsediments. Thus, upper layer (from water/sediment interface to 9 cm deep or so)is active sediment layer, and its below is non-active layer. The bacteria dynamicprocesses in sediments related with N-cycle generally occur in the active layer.Appropriate operational measures may be considered and these may be helpful tomaintain and fully utilize activity potentials of active layer so as to enhance pondmaterial cycling and to minimize the fish pond silting-up.