The invention discloses a high-density fish and vegetable co-existing system which comprises fish tanks, a planting system and a water storage tank, wherein the planting system comprises hydroponic vegetable breeding grooves and river stone breeding beds; the fish tanks are connected with flow diversion tanks and a solid sewage separation tank; the solid sewage separation tank is connected with a bacterial sewage decomposition tank; the bacterial sewage decomposition tank is connected with the water storage tank; the water storage tank is connected with the flow diversion tanks through a water pump; the flow diversion tanks are connected with the planting system; the other end of the planting system is connected with the water storage tank through a pipeline. A fish breeding system is adopted for generating nutritional water, and the nutritional water is diverted into the planting system through the flow diversion tanks and provides normal nutrition for plant growth; large-scale high-density production can be realized and the efficiency is high; water subjected to multiple purification is relatively good in quality; breeding and planting system structures are independent; the co-existing system is simple in structure and convenient to manage and maintain; the breeding system is low in operation cost, low in energy consumption and environment-friendly; the co-existing system has the characteristics of simple structure, stability and convenience for mounting, maintenance and operation; diversity of culture of leaf vegetables and melon and fruit vegetables can be realized.