The contrast experiment was carried out about the effects of Bacillus subtilis and spinach(Ipomoea aquatica Forsk) on the water quality improvement in the pond during the co-farming of rice-crayfish-finless eel. The results showed that Bacillus subtilis and spinach both improved water quality, increased DO and decreased pH of water.Bacillus subtilis had better effects in the decreasing of the NH₄⁺-N, NO₂^--N, TN, TP than spinach of three density groups with the highest level of degradation rate by 68.06%, 86.49%, 49.96%, and 58.82% respectively. Generally, the spinach with 20% of density degraded the level of NH₄⁺-N, NO₂^--N, TN, TP by 63.00%, 88.39%, 53.12 and 49.02% most efficiently. In sum, the combination of Bacillus subtilis and spinach with the 20% density in the pond during the co-farming of the rice-crayfish-finless eel was better.