Purifying the water of culturing Pseudobagrus fulvidraco(Richardson) fry by using submerged plant Elodea Nuttalli and Hydrilla Verticiullata, two kinds of ecosystems which compounded with submerged plant and fish co-cultured were made, one is non exchanged water aquarium (static water), the other is exchanging water aquarium (dynamic water). The water quality index and the fry survival rate in the aquarium were tested and compared. The results show as follows:(1) the water is good in co-cultured submerged plant-fish aquarium and the fry is growing well. After 5 weeks feeding, the water quality index in the dynamic system are:DO (dissolved oxide) ≥ 8.0mg/L, NH₄⁺-N (total ammonia nitrogen) ≤ 0.34mg/L, COD (chemical oxygen demand) ≤ 18mg/L. SS (solid suspend grain) ≤ 12mg/L, the fry survival rate is 93.3%, and in the static system, the water quality index are:DO ≥ 7.5mg/L, NH₄⁺-N ≤ 0.92mg/L,COD ≤ 28mg/L, SS ≤ 20mg/L, the fry survival rate is 60%.(2) As contrast aquarium (without planting submerged plant), in the dynamic system, the water quality index are:DO ≥ 4.0mg/L, NH₄⁺-N ≤ 2.41mg/L,COD ≤ 66mg/L,SS ≤ 51mg/L, the fry survival rate is 66.7%, and in the static water the water quality worsened during the fry rearing, the water quality index are:DO ≥ 2.5mg/L. NH₄⁺-N ≤ 3.22mg/L,COD ≤ 88mg/L, SS ≤ 55mg/L, the fry survival rate is 60%. the fry survival rate is only 6.7%.