Slow-release large-particle urea fertilizer and preparation method

The invention relates to nitrogen fertilizers, in particular to a slow-release large-particle urea fertilizer and a preparation method. The fertilizer comprises urea, a slow-release agent and synergist, and the slow-release large-particle urea fertilizer with 1.5-4.5mm grain diameter is obtained through tower granulation. By weight percentage, the urea: the slow-release agent: the synergist is equal to 1: 0.001-0.1: 0-0.5. The slow-release agent is a urinary enzyme inhibitor and a nitrification inhibitor (ammonium stabilizer), the weight part of the urinary enzyme inhibitor to the nitrification inhibitor is equal to 0.5-2: 0-2, and the synergist is polyaspartic acid or polyaspartic acid salt. The slow-release large-particle urea fertilizer is suitable for various plants and soils, has remarkable disease-resistant, drought resisting lodging-resistant effects to crops, effectively improves nutrient storing capacity of the soils, has strong effect to following crops, and can enable production of grains to increase by 8-15%, enable production of vegetables to increase by 14-40% and enable production of commercial crops to increase by 10-20%.