The invention discloses a preparation method of nano petaline Ni(OH)2. The method comprises the steps of taking nickel sulfate and urea as materials, preparing mixed solution of which the molar ratio of nickel to urea is 1:1 to 1:6 and then transferring the mixed solution to a 200mL of self-pressure lining polytetrafluoroethylene stainless steel reaction kettle, wherein the loading degree of a hydrothermal reaction kettle can be up to 80%; covering an inner cover and an outer cover to feed to an electric heating constant-temperature tank, heating the solution to 170 DEG C, reacting for 2-20 hours at constant temperature, then naturally cooling the solution to room temperature, filtering and washing the solution into a neutral state by deionized water; drying the solution into constant weight at 80 DEG C, and thinning the petals to prepare the nano petaline Ni(OH)2. According to the preparation method, the urea is taken as a precipitator, and a nano petaline Ni(OH)2 microsphere is directly prepared by hydrothermal syntheses; the method is simple in process, low in cost and easy to control without high-temperature sintering or a template agent, the obtained product crystal particle has the advantages that the size is uniform; the particle purity is high; the dispersity is good, and the crystalline form is good and controllable.