The invention discloses a natural compound preservative for preserving beverages. The natural compound preservative is prepared from a radix salviae miltiorrhizae extraction solution, a smoked plum extraction solution and a cinnamon extraction solution, so the natural compound preservative has a good bacteria resisting and restraining effect and has a good preservative effect. The raw materials adopted for the natural compound preservative all come from natural plants, and the preservative prepared from the natural plants has a quite small toxic and side effect on a human body and even has notoxic or side effect. A grinding device for grinding the raw materials into powder completes the process of automatically cutting and grinding objects needing to be ground, and is simple in structureand easy to operate. A sieve plate is installed in the device, and work efficiency is improved. According to the grinding device, a replacing channel is arranged on a grinding box body, the sieve plate, a new movable grinding plate and a new fixed grinding plate can be conveniently installed and replaced. A first grinding edge is installed on the movable grinding plate, and a second grinding edgeis installed on the fixed grinding plate, so that the grinding efficiency is high, and the grinding effect is good.