The invention discloses an arrangement structure of the main loop of a nuclear power plant reactor coolant system. The arrangement structure includes a reactor plant, a pressure vessel, steam generators, a pressure stabilizer, main pumps and main pipelines; a raft foundation bottom plate is arranged in the reactor plant; the pressure vessel is installed in the reactor plant and is located above the raft foundation bottom plate; the main pipes are connected between the pressure vessel, the steam generators and the main pumps, so that the main loop can be formed; the pressure stabilizer is arranged on the main pipelines; and the height difference L of the center of the main pipelines which is connected with the pressure stabilizer and the upper surface of the raft foundation bottom plate in the reactor plant ranges from 9.7 m to 10.8 m. Compared to the prior art, and according to the arrangement structure of the present invention, the sinking arrangement of the main loop is adopted, and therefore, the seismic acceleration of a reactor fuel assembly can be increased to 0.3 g or above under a condition that the size of the structure of the reactor fuel assembly is not increased, and therefore, the seismic capacity of a reactor can be improved and can achieve internationally recognized seismic requirements for three-generation nuclear power technologies.