The invention relates to a biodiesel preparation method, which comprises the following steps: 1)oil and fatty alcohol enable an ester interchange reaction under solid alkali condition of a ZnO/Ca(OH)2/KF, KF/MMT and Na2SiO3 mixture; 2) evaporating fatty alcohol in the reacted mixture, separating glycerin; 3)adding one or more nonionic surfactant in the mixture as a filter aid, separating glyceryl monoaliphatic ester through a ceramic membrane to obtain the high purity biodiesel. The method has the advantages of simple process, strong raw material adaptability and accumulation prevention of saponification substance; oil utilization rate can approach 100%, the biodiesel purity is high, post-treatment is simple, vacuum distillation can be avoided, concentration of the by-product glycerin is high, temperature and pressure required by the ester interchange reaction are low, cost is reduced, biodiesel yield is high, and water-bath heating is used for keeping constant reaction temperature.