Abstract: In order to examine the influences of different fish/vegetable ratio on water pollution factors such as inorganic nitrogen (N) and phosphorus (P), a laboratory scale aquaponics system based on siphon principle was designed as follows:The number of Ipamoea batas in hydroponics box was fixed, while the number of Oreochromis niloticus in culture box was changed as a fish/vegetable ratio of 6:10, 8:10 or 10:10, respectively; The water pH, dissolved oxygen (DO), inorganic N (including NH₄⁺-N、NO₂^--N and NO₃^--N) and inorganic P contents were analyzed at different time of the experiment.The results showed that the content of NH₄⁺-N was positively correlated with the number of fish in the early stage of the experiment, and maintained stable at a lower content afterwards with nutrient cycling; The NO₂^--N content in the water maintained at a very low level and was unaffected by fish/vegetable ratio; The accumulation of NO₃^--N and PO₄^3--P contents were significantly correlated with plant and fish growth and was influenced by fish/vegetable ratio.Therefore, choosing a right fish/vegetable ratio would be crucial to a long-term health of the aquaponics system.