The invention belongs to the field of drug preparations, and particularly relates to a sustained-release drug and a preparation method thereof, and in particular relates to metaxalone tablets and Zileuton sustained-release tablets prepared by using the method. The sustained-release drug contains a water non-soluble material. Compared with the prior art, on the premise of achieving a same drug release control effect, the consumption of auxiliary materials is at least decreased by 10 to 20 percent and even by more than 50 percent, so that the size of a final preparation is obviously reduced, and the final preparation is easy to swallow.