The invention discloses a zirconium diboride-based composite material toughened by colloid-dispersed chopped carbon fibers and a preparation method thereof and belongs to the technical field of ultrahigh-temperature ceramic-based composite materials. The zirconium diboride-based composite material is prepared from the raw materials including, by mass, 1-3 parts of the chopped carbon fibers, 15-25 parts of nano zirconium diboride powder, 1-3 parts of nano silicon carbide powder, 1-5 parts of phenolic resin, 0.1-0.5 parts of polyethyleneimine, and 60-100 parts of anhydrous ethanol. In the invention, the phenolic resin and the polyethyleneimine are subjected to a crosslinking reaction, wherein the short carbon fibers are uniformly dispersed in the colloid, thereby overcoming a problem of abrasion of the fibers during conventional ball-milling material blending. Through the colloid dispersion method, a high-temperature protective layer is formed on the surface of the carbon fibers, and further degradation rate during high-temperature sintering of the carbon fibers is reduced, interface bonding among fiber substrates is weakened, and debonding, bridge connection and pulling-out of the fibers are promoted. The zirconium diboride-based composite material has high compactness, high strength and high toughness.