The invention discloses a method for preparing biodiesel with hodgsonia macrocarpa as a raw material. The method comprises the following steps of adding a zeolite molecular sieve adsorbent to carry out pretreatment on hodgsonia macrocarpa oil to obtain hodgsonia macrocarpa; adding pure hodgsonia macrocarpa oil, methyl alcohol and a magnetic nanometer catalyst into a reaction kettle according to the weight ratio of 100:(30-40):(1.5-2.0) to be subjected to an esterification reaction; separating and purifying crude biodiesel products to obtain biodiesel. The magnetic nanometer catalyst is introduced into the esterification reaction, catalytic efficiency is high, the catalytic effect is remarkable, reaction time is shortened, and the yield of the biodiesel is increased; the magnetic nanometer catalyst can be separated and recovered conveniently and fast according to an external magnetic field, and can be reutilized many times. The method has the advantages that the preparation technology is simple, energy is saved, environment is protected, the reaction time is short, the yield is high, and the product purity is high, the method has good social benefits, ecological benefits and economic benefits, and large-scale industrialized production can be achieved easily.