The present invention relates to a preparation method of eggplant sauce. The preparation method includes the following steps: 0.5 kg of eggplant, 0.1 kg of rhizoma imperatae, 0.1 kg of reed rhizome, 0.05 kg of moss, 0.02 kg of radix astragali, and 0.02 kg of poria cocos are weighted, the weighed raw materials are washed clean, the washed raw materials are chopped into granules with a diameter of less than 4 mm, the chopped raw materials are respectively blanched by boiling water, and the blanched raw materials are air-dried for standby applications; a soaking liquid is prepared; 0.05 kg of shallot, 0.05 kg of chili, 0.05 kg of garlic, and 0.05 kg of fresh ginger are washed clean, the washed raw materials are chopped into granules with a diameter of less than 2 mm, and 0.25 kg of the soaking liquid is added; 0.1 kg of honey is added and the mixture is stirred evenly; the stirred mixture is mixed and stirred evenly with the water blanched and air-dried primary sauce body; 0.05 kg of green soybean and 0.1 kg of beef are weighed, the green soybeans are soaked to be swollen using water, the beef is diced into blocks as the sizes of the green soybeans, the diced beef and green soybeans are put into a pot together, water at three amount of the diced beef and green soybeans is added, the mixture is simmered for 60-70 minutes, then 0.05 kg of vegetable oil, 0.05 kg of edible salt and 0.15 kg of the unused soaking liquid are added into the pot, and after the mixture is simmered, the mixture is cooled for standby applications; and earth burnt or glass containers are taken, the containers are washed clean, the washed containers are disinfected, the products are stirred evenly, the stirred products are sealed for 15-20 days, and lids are opened to prepare the eggplant sauce.