The present invention discloses a highly cut-resistant ultrahigh molecular weight polyethylene fiber, made of a ultrahigh molecular weight polyethylene and an inorganic ultrafine micropowder having a nanocrystalline structural morphology, wherein the inorganic ultrafine micropowder is one of an oxide, carbide, and nitride of aluminium, titanium, silicon, boron, and zirconium, or a combination thereof, and has an average diameter of 0.1-300 μm and a content of 0.1-14% of the total weight of the fiber. The present invention further discloses a method for preparing a highly cut-resistant ultrahigh molecular weight polyethylene fiber, comprising: adding nanocrystalline silicon carbide particles to a solvent, and repeatedly grinding by a sand mill; adding a ultrahigh molecular weight polyethylene, and the silicon carbide nanoparticles to a solvent, and mixing until uniform by stirring by a homogenizer with high shear, to obtain a spinning solution; and subjecting the spinning solution to conventional gelation spinning, and extracting and hot drawing the gel filament spun, to obtain a composite fiber. In the present invention, by introducing the nanocrystalline ultrafine particles into the ultrahigh molecular weight polyethylene fiber, the composite fiber of ultrahigh molecular weight polyethylene/nanocrystalline ultrafine particles has a quite excellent cut-resistant performance.