Steel slag compound fertilizer and preparation method thereof

The invention provides a steel slag compound fertilizer and a preparation method thereof, and relates to the technical field of environment-friendly agriculture. The preparation method includes the following steps: 1) accurately weighing steel slag, mineral slag and dust ash according to the mass ratio of the steel slag to the mineral slag to the dust ash of (30-80):(0-60):(10-30), adding the weighed raw materials into a stirring machine, and performing stirring at the speed of 150-250 r/min for 5-15 min; 2) adding a fertilizer effect correction agent according to the element proportioning requirement of total nutrients N+P2O5+K2O of >=25%, wherein the correction agent is one or a combination of two or more selected from urea, ammonium hydrogen phosphate, ammonium dihydrogen phosphate andphosphorous-containing gypsum, adding the weighed various raw materials into a stirring machine, and performing stirring at the speed of 150-250 r/min for 5-15 min to obtain a crude compound fertilizer; and 3) performing coat