Abstract: Chinese mitten crab was stocked in the East Lake Reservoir with area of 2700 hm2. The zoobenthos and aquatic plantswere measured before and after stocking crab,and the effects of the crab on the zoobenthos and aquatic plants were studied by theway of ANOVA. The Chinese mitten crab carrying capacityof reservoirs and lakes depends on the biomass of different zoobenthosand macrophytes. The study also analyses the crab food selection of different natural diets in East Lake Reservoir. In 2001,withstocking amount of crab of 1500kg,the mitten crab(220ind1kg-1) had noticeable effects on chironomus and oligotricha,and littleeffect on other mollusca and aquatic plant,at the stocking density of 122ind1hm-2. In 2002,with stocking amount of crab of 3500kg,the mitten crab of same size(220ind1kg-1) had significant effects on zoobenthos and some submersed macrophyte, at thestocking density of 285ind1hm-2. The ideal stocking amount is that,after stocking crabs,the structure and function of aquaticecosystem still can be maintained,the food resources of the crab were not damaged seriously,particularly the zoobenthos and submersed macrophyte. Therefore,the carrying capacity,in large lakes and reservoirs,is defined as the maximal standing biomass ofthe crab in the case that the growth of aquatic vegetation and zoobenthos were not significantly affected by the crab. The authorsthink that the stocking amount of crabof East Lake Reservoir should not be beyond 1500kg. The researchof crab carrying capacity in East Lake Reservoir gives an exploration sample of other waste shallow water area in high frigid zone.