The invention discloses a preparation method of a liquid ferment. The preparation method comprises the following steps: mixing mango kernels, loquat kernels, lychee kernels, peach kernels and longan kernels, grinding the mixture, soaking the mixture in an ethanol water solution for 8-10 hours, extracting a soak solution, adding water to dilute, and filtering to obtain first separation liquid; mixing shaddock peels, apple peels, guava peels, echeveria macdougallii leaves, sugar orange peels, melon peels, unpeeled pawpaw and a brown sugar water solution, carrying out braising and pulping to obtain syrup, fermenting to obtain a first fermented substance, and filtering, so as to obtain first fermentation liquid and first fermentation residues. The utilized raw materials of the liquid ferment include nutrient-rich fruits such as avocados, carambola, green plum pulp, haws, mulberries and the like and further include polygonatum sibiricum capable of well treating weakness of the spleen and the stomach, body fatigue and debility, strengthening bones and musculatures and benefiting marrow as well as radix stemonae capable of moistening lung, relieving cough and eliminating phlegm, and polygonatum sibiricum and radix stemonae are two Chinese herbal medicines with very high medicinal values, so that the liquid ferment has very good health efficacy.