The invention relates to the technical field of chemical industry, and discloses a method for preparing a special fertilizer for pears and preparing potassium dihydrogen phosphate as a byproduct. The method comprises the following steps: reacting phosphoric acid with carbomite by analyzing nutritional elements required by pears to prepare an intermediate, reacting the intermediate with an alkaline potassium salt to prepare potassium dihydrogen phosphate, controlling the content ratio of nutrients in a filtrate in the potassium dihydrogen phosphate crystallizing process, and adding trace element compounds to the potassium dihydrogen phosphate separated filtrate in order to prepare the special fertilizer for pears. The special fertilizer for pears, prepared by analyzing the ratio of the nutritional elements required in the growth process of pears, improves the output of pears, and the prepared potassium dihydrogen phosphate has high purity and has a relatively low cost.