The invention relates to the technical field of black tea preparation, and particularly relates to a black tea preparation method capable of improving the content of tea polyphenol. By the steps of classifying, processing, mixing and twisting the tea leaves, carrying out fixation, twisting again, unbinding, fermenting, reshaping, carrying out fixation, drying, sterilizing and the like, nutritional components in the tea leaves are subjected to great microcosmic change, the nutrition structures in the tea leaves are enriched and relative high nutritional substance leaching rate is achieved; technological parameters are controlled properly, so that the nutrient elements in green tea leaves are controlled effectively, and harmful substances in the tea leaves are discharged out in the preparation process; useful substances, namely tea polyphenol and the like are converted and retained, the content of tea polyphenol and similar substances (condensed polyphenols) in prepared black tea is relatively high, and the health function of tea leaves is enhanced; according to testing, the content of polyphenols in the black tea is improved by 17-19% compared with that in the traditional black tea.