A low-cost high-coercivity LaCe-rich neodymium-iron-boron permanent magnet, and a preparation method therefor and the use thereof are provided. The permanent magnet is prepared by mixing and sintering an LaCe-free and HRE-free neodymium-iron-boron main phase alloy and an LaCe-M alloy. An LaCe-free main phase alloy and an LaCe-M auxiliary phase alloy are respectively smelted at first, and then, the same are subjected to powder preparation, mixing, pressing, and sintering, thereby avoiding LaCe entering main phase crystal grains. The depth and concentration of HRE diffused into the magnet are effectively improved by using the characteristics of a low melting point and high flowability of an LaCe-rich crystal boundary phase, thereby improving the uniformity of components and structure distribution in the magnet.