The invention provides a fertilizing method returning straw to a wheat-corn double-cropping field to replace potassium, belongs to the technical field of fertilizer, and aims to solve the problem thatdue to the fact that high crop yield is excessively pursued, element deficiency exits in crop growth and the like in current agricultural production, excessive fertilizer is applied. The fertilizingmethod capable of reducing potassium fertilizer application has the advantages that by returning all straw to the field, potassium in the straw is used to partially replace potassium in chemical fertilizer, and accordingly, fertilizer use amount can be reduced, potassium fertilizer resource shortage can be relieved, and high-efficiency straw utilization and environment-friendly agricultural production are achieved. Experiment results show that the fertilizing method can increase crop yield and effectively increase soil fertility as compared with methods which do not return straw to fields andconventional methods returning straw to fields.