The invention relates to a preparation method of fish-mutton soup. The preparation method comprises the steps of: dicing the mutton, adding water and anise, then boiling, deboning, taking the meat on the back of the fish, putting the fish head and the fish bones into an oil bath, frying, and then putting into a slow cooker, adding water, boiling, then adding the deboned mutton, the mutton bones and the fried fish head and the fried fish bones, adding a seasoning bag, and then boiling until the soup becomes milk white to obtain the fish-mutton soup. The fish-mutton soup does not have the smell of fish and the smell of mutton, is savoury and mellow in taste, tasty but not greasy, rich in various inorganic salts necessary for a human body, such as calcium, phosphorus, ferrum, iodine and the like, and has the advantages of warming the stomach, expelling the coldness, improving the taste, enhancing the kidney and tonifying Yang, smoothening the skin and the like.