The invention discloses a rainwater collecting pool and a construction method thereof. The rainwater collecting pool comprises a flow abandoning pool and a modular pool; a flow abandoning pool filterscreen is arranged at the middle part of the flow abandoning pool; the flow abandoning pool is divided into a dirt filtering area and a precipitating area by the flow abandoning pool filter screen; one end of the flow abandoning pool is a water inlet, and the other end of the flow abandoning pool is a water outlet; the water outlet is connected with a water outlet pipe; the water outlet pipe is connected with the modular pool; water storage grid layers are uniformly distributed in the modular pool; inspection wells communicating with the water storage grid layers are symmetrically arranged atthe two ends of the water storage grid layers; dirt discharge pumps are arranged at the bottoms of the inspection wells; one inspection well is connected with the water outlet pipe; a sand settling pool is arranged at the bottom of the other inspection well; and an overflow port is formed in the side wall, near one end of the sand settling pool, of the modular pool. The rainwater collecting pool can effectively collect and store rainwater; and through wide application of rainwater collection and utilization, rainwater is retained or infiltrated underground, so that the displacement is reduced,the urban flood disaster threat is relieved, underground water is supplemented, the water environment is improved, and the ecological environment is repaired.