Disclosed is a method for preparing high purity biodiesel from crude oils. The method comprises the steps of: pre-treating the crude oil raw material to remove impurities; pre-esterifying the pre-treated crude oil raw material under the effect of a catalyst of concentrated sulfuric acid; and then carrying out an ester exchange reaction in the presence of an alkali catalyst; recycling methanol, and separating glycerol, so as to obtain a crude fatty acid methyl ester; and subjecting the obtained fatty acid methyl ester to purification, distillation and segmentation to obtain a high-purity fatty acid methyl ester.