The invention provides a spray-drying method for preparing metoprolol succinate sustained-release capsules. The method comprises the following steps of: (1) dispersing metoprolol succinate in an oil phase uniformly, and emitting ultrasound to obtain a suspension, wherein the oil phase contains 1 to 10 percent of surfactant; (2) dissolving a macromolecular capsule material in an aqueous solution of ethanol, adding an antisticking agent, a plasticizer and a dispersing agent, stirring uniformly, filtering and preparing an external water phase for later use; and (3) adding the suspension obtainedin the step (1) into the ethanol solution obtained in the step (2), homogenizing and emulsifying to obtain a metoprolol succinate suspension/oil/water (S/O/W) multi-emulsion spray liquid, and spray-drying. The metoprolol succinate sustained-release capsules are rounded in appearance, smooth and clean in surfaces, high in flowability and encapsulation rate, lasting in medicinal effect and high in stability, have the grain diameter of between 30 and 300 micrometers, can control burst release effectively, have an obvious sustained-release effect, and are suitable for large-scale industrial production.