The invention relates to a preparation method of 4,4-dihalotetrahydropyran, comprising the steps of mixing halogenated homoallylic alcohol, aldehydes, indium trihalide and a solvent in a flask, mixingwell to obtain a mixed liquid controlled to be -20 to 0 DEG C, dropwise adding trimethyl halogenosilane slowly, starting reaction, allowing reacting by stirring at a certain temperature for 1-24 h, adding sodium bicarbonate saturated solution for quenching reaction, after the solution layers into an organic phase and an aqueous phase, extracting the aqueous phase with methyl tertiary butyl ether,combining the extract to the organic phase, washing the obtained organic phase with saturated salt water, drying, evaporating to remove an organic solvent to obtain a crude product, and subjecting the crude product by separation and purification by column chromatography to obtain a finished product that is applicable to the field of flame retardants and the field of pesticides. The preparation method has simple process and high yield of product, the product has high purity, indium trihalide of catalyst quantity is used in the reaction system, indium consumption is low, the catalyst cost is low, and the preparation method is economical and practical.