The invention discloses a method for preparing sodium dihydrogen phosphate by utilizing phosphoric acid by wet process. The method comprises the steps of carrying out reaction on carbamide and the phosphoric acid by the wet process to obtain intermediate, and then carrying out a reaction on the intermediate and sodium hydroxide to obtain the sodium dihydrogen phosphate product. The method is short in process route, low in energy consumption, stable in product quality, low in production cost, convenient to operate and safe in production; the by-product slurry can be completely recycled; the whole production process is environment-friendly, clean and free from pollution as well as emission of waste gas, waste water and waste residue; therefore, the method responses to the policy of energy conservation and emission reduction as well as clean production, and solves the problems of complicated technology, unstable product quality, high energy consumption, environmental pollution and the like in the prior art; the obtained sodium dihydrogen phosphate product has the purity of more than or equal to 98%.