Preparation method for in-situ coated controlled-release fertilizer urea slow-release particle fertilizer

The invention relates to a preparation method for an in-situ coated controlled-release fertilizer urea slow-release particle fertilizer, which comprises the steps of arranging particle urea in a fluidized bed coating machine, switching on a power supply to enable the particle urea to be in a fluidized state, and then opening a heating switch to lead the particle urea to be in air of 80 DEG C to 110 DEG C; spraying a formaldehyde solution with potential of hydrogen (pH) of 1 to 5 and mass concentration of 20-37% through a spray gun on the surface of the particle urea to form first even films; and spraying a mixed solution between formaldehyde and the urea through the spray gun continuously on the surface of the urea to form even coatings, and achieving the urea slow-release particle fertilizer. The preparation method uses in-situ reaction between the formaldehyde and the surface of the particle urea to form films to prepare the coated slow-release fertilizer, thereby having the advantages of being simple in process and low in price. The mixed solution of the formaldehyde and the urea is used as a coating agent so as to enable the mixed solution to perform in-situ reaction on the surface on the particle urea to prepare the coated slow-release fertilizer. Slow-release fertilizers with different slow-release periods can be prepared according to thickness of films.