The invention discloses a puerarin liquid preparation and a preparation method thereof. The method comprises the following steps: puerarin is dissolved in water and then added with an iso-osmotic regulator, thus obtaining a solution I by mixing evenly; the solution I is filtered with the aperture of 0.22 Mum, thus obtaining a filtering solution a; the filtering solution a is treated with ultrafiltration by an ultrafiltration membrane with the MWCO of 10000 Dalton, thus obtaining a filtering solution b; the filtering solution b is filtered by the aperture of 0.22 Mum, thus obtaining a filtering solution c; and the filtering solution c is filtered by the aperture of 0.22 Mum, thus obtaining the puerarin liquid preparation. The preparation method of the puerarin liquid preparation overcomes the defect that the existing preparation has a plurality of untoward reaction factors. Experiments prove that the preparation prepared by the method does not contain a solubilizing agent, the content of other particles and bacteria is low, the puerarin has high purity and good stability; in addition, products of each batch produced by the method of the invention meet quality standards, have batch to batch stability and reliable quality; the method of the invention has simple process and is convenient for production operation and control and suitable for mass production.