A preparing method of a miglitol intermediate

The invention belongs to the field of medicine synthesis, and relates to a preparing method of a miglitol intermediate. The method includes performing Swern oxidation by adopting tetrabenzyl glucose diol as a raw material to obtain a tetrabenzyl glucose dicarbonyl derivative, and directly subjecting the oxidation product without separation to a double reductive amination reaction with ethanolamine and sodium cyanoborohydride under the existence of a dehydrant to prepare tetrabenzyl miglitol that is an important intermediate for preparation of miglitol. The method is mainly advantageous in that: the tetrabenzyl glucose dicarbonyl derivative which is instable is directly used for the reaction in the next step without separation; proper reaction conditions are selected in the double reductive amination reaction step to directly obtain an optically pure target product 2-position of which is in an R configuration; steps of separation and purification for an enantiomer mixture are omitted, and loss caused by the steps is omitted; and the method is short in reaction time and high in yield.