The invention relates to the technical field of chemical industry, and discloses a method for preparing a dendrobium officinale nutrient fertilizer. The method comprises the following steps: determining the proportion of nutritive elements in the dendrobium officinale nutrient fertilizer by analyzing various nutritive elements absorbed in a growth process of dendrobium officinale, reacting phosphoric acid with carbamide to generate an intermediate, then introducing ammonia gas into the intermediate to produce ammonium dihydrogen phosphate, separating part of ammonium dihydrogen phosphate by crystallization so as to control the content of nitrogen and phosphorus in a solution to meet the proportion required by the growth of dendrobium officinale, and then adding potassium and other medium trace element compounds into the solution to prepare a fertilizer special for dendrobium officinale. According to a production method disclosed by the invention, raw materials can be fully used, produced ammonium dihydrogen phosphate is relatively good in quality, and the prepared fertilizer special for dendrobium officinale is relatively low in cost.