The invention relates to a preparation method of a traditional Chinese medicine, in particular to a drug for treating prostatitis and a preparation method thereof. The preparation method is that 1600g of herba epimedii, 800g of raidx astragali, 600g of cattail pollen, 800g of plantain and 200g of medicinal cyathula root are used as bulk pharmaceutical chemicals and the preparation method comprises the following steps: taking a defined amount of herba epimedii, raidx astragali, cattail pollen, plantain and medicinal cyathula root to add 2000g of water to perform hot reflux and extraction for 2.5 hours, reducing pressure and concentrating the product into thick paste at the temperature of 60 DEG C, performing vacuum drying at the temperature of 60 DEG C, pulverizing into fine powder, mixingthe fine powder with auxiliary materials to prepare capsules. The drug prepared by the invention has high-content effective components; the preparation efficiency and the yield are improved compared with the traditional technology; the effective components are not decomposed in the preparation process; and the content of the effective components are reserved to greatest degree, thus improving thebioavailability of the drug and having obvious advantages compared with the drug prepared by the original method.