The invention discloses a mask-shaped porous NiO nanometer compound material and a preparation method thereof. Mask-shaped NiO nanometer sheets are synthesized through a two-step method, so that the obtained NiO nanometer sheets are uniform in size; a solvent for preparation is deionized water which is environmentally friendly without pollution; a used device is simple and easy to operate, and a precursor can be grown in situ in a high pressure reactor; a preparation process is easy, the used device is simple, and the material is pollution-free and can be produced macroscopically.