The invention discloses a preparation method of a urea-phosphate-containing multielement water-soluble fertilizer, which comprises the following steps: (1) adding phosphoric acid with the concentration of greater than 75% and urea into a vacuum dryer according to needs, keeping the vacuum degree at 0-0.08 MPa, and heating to 90-140 DEG C to form a hot urea phosphate solution; (2) sending the hot urea phosphate solution to a mixing reactor, adding a mixed fertilizer into the reactor, and carrying out mixing reaction to obtain a mixed slurry; and (3) sending the prepared mixed slurry into a spray drying tower, and carrying out spray drying to form the powdery urea-phosphate-containing multielement water-soluble fertilizer product. The preparation method disclosed by the invention has the advantages of short technical process and low cost, is simple and convenient to control, and can easily implement industrialization. The powdery urea-phosphate-containing multielement water-soluble fertilizer product obtained by the method has the advantages of uniform appearance and nutrients, no retarded reaction and low tendency to hardening.