The invention relates to the chemical catalysis field, in particular to a preparation method of a specific catalyst for preparing biodiesel, namely, a zinc oxide nano fiber catalyst doped with rare earth salt. The preparation method is characterized in that organic acid, polyvinyl alcohol, zinc acetate and transition metal salts are mixed into zinc oxide nano fiber stock solution doped with the rare earth salt according to weight percent. When the voltage is 5-10kV, the distance between a spinneret and a receiving device is 10-20cm, the feeding velocity is 3-5ml/1h and the electro spinning temperature is 40-50 DEG C, an electrostatic spinning instrument is used for preparing zinc acetate/ transition metal salts/ polyvinyl alcohol composite fiber in an electro spinning way. The zinc acetate/ transition metal salts/ polyvinyl alcohol composite fiber is put in a muffle furnace for high temperature calcination and is kept for 3-5h under 500-600 DEG C. Then, the zinc oxide nano fiber doped with the rare earth salt is obtained. The method for preparing the zinc oxide nano fiber doped with the rare earth salt has the advantages of simple equipment, easy operation and large scale preparation. Used for the biodiesel preparation through catalytic oil alcoholysis reaction, the preparation method is characterized by mild condition, light corrosion on the equipment, less waste liquid production, low pollution on the environment and repeatable utilization of the catalyst.