A method for preparing a cheap light rare earth lanthanum cerium iron boron nano-crystal permanent magnet belongs to the field of rare-earth permanent magnets. The method includes: performing matching according to (Lax/Ce1-x) yFe14B, x=0-1, y=2.0-4.0 element mole ratio, putting the matched material into a suspension smelting furnace, performing heating and smelting in the argon atmosphere, and acquiring an even ingot casting; performing mechanical grinding on the ingot casting to remove surface oxide, performing smashing, and filling the ingot casting fragments in a quartz tube; arranging the quartz tube filled with the ingot casting on a melt rapid quenching device to perform melting, spraying alloy fluid to a copper roller which is rotating at a high speed from a nozzle, allowing the alloy fluid to contact the copper roller to be rapidly cooled, and acquiring a rapid quenching band; and screening the rapid quenching band to remove impurities, smashing the rapid quenching band and performing screening, putting the smashed rapid quenching band in a die, putting the die in a discharging plasma sintering furnace, and performing hot pressing sintering at a suitable temperature and pressure. The method can easily achieve rapid sintering of materials, and can acquire compact ultra-fine crystal even nano-crystal sintering body.