The invention belongs to the field of metal materials and particularly relates to a preparing method of a boron-rich micro-nanosphere-strengthened copper-based composite. The preparing method comprises the steps that boron oxide (B2O3, >=98.0%) serves as a boron source, industrial pure copper is put into a high-frequency induction furnace to be heated to around 1500 DEG C first under the protection of inert gas, then preheated industrial pure aluminum is added, a graphite rod is used for slow stirring, and then preheated boron oxide is added; 10 minutes after a reaction is completed, Cu-B alloy is poured into a U-shaped die; then, the prepared Cu-B alloy is remelted at a high temperature and spun into strip-shaped materials with a single-roller chilling device at the rotating speed of 2000 r/min. The preparing method has the advantages of being simple in technological operation, low in cost and high in production efficiency; according to the boron-rich micro-nanosphere-strengthened copper-based composite prepared with the in-situ generation method, boron nanospheres are distributed in a matrix in a dispersion mode and well combined with the matrix, and thus the composition has high corrosion resistance and a good comprehensive mechanical property.