Preparation method of rounded grain potassium fertilizer

The invention provides a preparation method of a rounded grain potassium fertilizer. The method comprises the following steps that powdery potassium fertilizers are poured into a stirrer to be stirred; atomized water is added by a high-pressure spray nozzle while the stirring is performed, so that the atomized water and the powdery potassium fertilizers are fully blended in the stirrer; then, ureais sprayed on the surface of a mixed material formed by the potassium fertilizer and the atomized water in a spraying form by the high-pressure spray nozzle; a second mixture is formed; next, the second mixture is heated to be 100 to 120 DEG C; the uniformly mixed third mixture is fed into a double-screw extruder; finally, the mixture is extruded through an opening mold; after mixing reaction, compacted materials are extruded through the opening mold via an airflow granulator and are directly cut into grain materials; after the grain cutting, the materials are fed into a planer for planing and roughening. The prepara