The invention discloses a one-step preparation method of palladium ethylenediamine sulfate for electroplating and belongs to the field of fine chemicals. The method comprises the following steps: (1)adding reagent-grade palladium tetraammine sulfate into deionized water to prepare a solution A with palladium ion concentration of 20-150g/L; (2) adding 0.5-4 times of volume amount of deionized water into reagent-grade ethanediamine and diluting to prepare a solution B, wherein the mass-volume ratio of palladium tetraammine sulfate to ethanediamine is 100g to (63-252mL); (3) slowly adding the solution A into the solution B and reacting for at least 12 hours under negative-pressure condition until a large amount of yellow crystal sediment is generated; and (4) filtering and separating crystals, and drying the crystals under low temperature to obtain palladium ethylenediamine sulfate. The method is simple in process, few in by-products and high in yield; harmful impurities are not introduced in the preparation process, so that the purity of the product is high.