The invention relates to a potash fertilizer application method used in cooperation with wheat-corn crop rotation anniversary whole straw returning.The method mainly includes the steps of returning straw to the field after corn harvesting, sowing wheat seeds, applying fertilizer, sowing corn in a no-tillage mode after wheat straw is returned to the field and applying fertilizer, wherein under the condition that wheat and corn are at the high-yield level and in other words, the wheat yield is 400-600 kg/mu and the corn yield is 500-700 kg/mu and under the condition that all wheat straw and corn straw are returned to the field after grain harvesting, calculated as K2O, the anniversary potassium nutrient input is 9-13 kg/mu, the application amount of wheat season nutrients accounts for 27-45% of the anniversary amount, and the application amount of corn season potassium nutrients accounts for 55-73% of the anniversary amount.Returning of straw of crops of two seasons is fully considered, powerful potassium compensation is conducted on soil, the fertilizer application amount and the distribution ratio are determined according to potassium requirement rules of the two types of crops, potassium supply in different growth periods of the two types of crops is ensured, total amount regulation and control and staged planning and management are achieved, the method is effectively combined with cultivation and tillage measures, the potash fertilizer utilization rate is greatly increased, and potassium balance of the soil-crop system and sustainable utilization of lands are ensured.