The invention belongs to the technical field of beer brewing, and relates to a preparation method of a lotus root beer. The preparation method comprises three processes of lotus root juice preparation, wort preparation and mixed fermentation, and specifically comprises the following steps: washing away external silt and sundry fungi with a citric acid water solution, then feeding the clean lotus root into a steam furnace, steaming, cooling, saccharifying according to a conventional process method, performing enzyme deactivation on the saccharified lotus root sauce, and finally pressing and filtering through a conventional extrusion apparatus to prepare a lotus root raw juice; pulverizing malt, adding water, performing mash gelatinization, saccharifying, raking, standing, refluxing, washing, adding humulus lupulus into a mash kettle, clarifying, and cooling to obtain wort; and adding the lotus root juice in the post-fermentation process of wort-based beer making, fermenting, cooling, filtering, and clarifying to obtain the lotus root health care beer. The preparation method has the advantages of mature process route, simple processing and preparation and low production cost; and the prepared lotus root beer has rich nutrients and a pure bouquet, is refreshing and tasty, has the function and mouthfeel of a beer, and can achieve a health care effect.