The invention relates to a nano-nickel oxide electrode material for a supercapacitor and a preparation method thereof. Nickel acetate and water are added into a reaction container, dispersed evenly, transferred to a closed high-temperature reaction kettle, added with acetic acid, and reacted at 300-500°C. After 5-10h, powdery nickel oxide can be obtained by filtering, washing and drying. The prepared electrode material nano-nickel oxide for supercapacitor has a multi-layer stacked structure, its grain size is 5-10nm, and the thickness of the sheet is 20-50nm; The method is safe, non-toxic, easy to operate, high in efficiency, low in cost, and easy for industrial application, and the produced nano-nickel oxide has the characteristics of large specific capacitance, good conductivity, stable structure, good electrochemical cycle stability and the like.