A long-acting sustained-release preparation of a drug for treating Parkinson' s disease and a preparation method thereof. The long-acting sustained-release preparation is microspheres comprising rasagiline or a pharmaceutically acceptable salt thereof and a biodegradable and biocompatible high molecular weight polymer. The microspheres comprise microspheres with an average particle size of 0.5-5 mm and microspheres with an average particle size of 20-150 mm.