The utilization and protection of the submerged plant resources by pen-crab culturing in Nushan Lake from 1992 to 1994 are studied.The results are summarized as rollows: Crab food was mainly Potamogeton crispus L.Vallisneria spiralis L., P.maackianus A.Been, Ceratophyllum demersum L., P.malaianus.Mig.and Hydrilla verticiliata Royle.etc, among which the frequencies of participation and the ideal biomass of P.crispus and H.verticiliata reach their highest point in Apr., May, June, July, Aug, and Sept., respectively.The changes of species composition and biomass of the submerged plants were closely related to the density of the crabs cultured, a density of crabs below 30ind·hm^-2 significantly results in an increase of the biomass of the submerged plants as well as the dominating group.The submerged plants resources could be reasonably used and protected by large-scale crab cultured only at an appropriate density such as 30ind·hm^-2 inside the pens in Nushan Lake.