A grinder for preparing brewing materials has a main casing, a grinding assembly and an unloading assembly to measure the amount of the brewing powder to unload. The unloading assembly has an unloading motor and a measuring barrel. When the user puts the brewing materials into the main casing, the grinding assembly grinds the brewing materials into the brewing powder. The brewing powder drops into the unloading assembly. When the unloading motor actuates the measuring barrel rotates, the brewing powder is deposited in a partafilter. Therefore, a user can grind tea leaves, Chinese herbal medicine, the petals and so on to have fresh brewing powder. Brewing liquids with the fresh brewing powder keeps the nutrient content and flavor. In addition, the bags for packaging the brewing powder is no longer needed to reduce environmental pollution and packaging cost.
