The invention discloses an integrated rainwater system for a sponge city and a construction method of the rainwater system. The rainwater system comprises a middle green belt and water storage tanks, wherein the middle green belt comprises a vegetation planting area and a rainwater infiltration area; a concrete course is arranged at the lower end of the rainwater infiltration area; a rainwater pipe is arranged at the lower end of the concrete course, and the rainwater pipe is connected to the water storage tanks; water pumping pipes are connected from the interiors of the water storage tanks; bidirectional nozzles are arranged at the other ends of the water pumping pipes; and water pumps are connected to the water pumping pipes. In accordance with the shortcomings of the prior art and the characteristics of the sponge city, the rainwater system, which integrates water seepage, water storage, water purification and utilization, is designed, and the construction method of the rainwater system is correspondingly designed; by promoting the water seepage with the adoption of vegetation, the problem of road water-logging is solved through slow discharge and controlled release; and in addition, some impurities in the rainwater are separated on the basis of the purification capacity of the vegetation, and the rainwater is stored in the water storage tanks and is used for spraying roads and watering the vegetation in dry season, so that adverse effect caused by drought and flood seasons can be effectively relieved.