The invention belongs to inorganic nanometer material field, especially relates to a method for preparing a ferrious noncrystalline nanometer simple substance, comprising the following steps: weighing two solids of A and B, respectively preparing solution B and solution A having concentration of 0.1-0.4mol/L, the mol concentration ratio of solution A and solution B is 1:1; adding deionized water in solution A, implementing ultrasonic concussion to generate mass air bubbles in the solution and when the air bubbles disappear, stopping the ultrasonic concussion and the reaction, then adding with the solution B to react in a centrifugal machine, wherein the reaction time is 2 -5 minutes, and finally getting black sediments, after washing to obtain the required product. The solid A is KBH4 powder, solid B is any one of FeCl2(or FeCl3), NiCl2.6H2O or CoCl2.6H2O etc. The solution A is KBH4 water solution, the solution B is any one of FeCl2( or FeCl3) ethanol solution, NiCl2 ethanol solution or CoCl2 ethanol solution etc. The invention has advantages of easily obtaining raw material, low cost and simple operation and equipment, small and even grain size of the product, is easy to industrialize, and can provide new approach and way for the synthesis of nanometer material.