The invention is a preparation method for nano material. The method of the invention can be divided into two steps, namely, processing flaky material and smashing flaky material; the method disclosed is that under high vacuum state, high temperature generated by electron guns and a molybdenum boat is adopted to gasify metal, metal oxide, fluoride and semiconductor, semiconductor oxide, semiconductor nitride and fluoride or to carry out gasification by putting a plurality of matters into a plurality of electron guns and molybdenum boats; the vapour is coagulated into flaky material on a flaky material collector and then the flaky material is taken down from the collector and then pneumatic cracking and ultrasonic cracking are carried out; finally the pure nano material is obtained. The technique can provide powder of nano material with high purity for a market.