The invention discloses a preparation method of a supercapacitor electrode material with good electrochemical performance, which takes a carbon cloth as a flexible substrate and grows a transition metal double hydroxide on the substrate. The invention particularly relates to a novel method for preparing a carbon-based nickel-cobalt double hydroxide supercapacitor electrode material by carbonizingcotton cloth at high temperature and growing nickel-cobalt double hydroxide on the carbonized cotton cloth by a one-step hydrothermal method, wherein the carbon-based nickel-cobalt double hydroxide supercapacitor electrode material is prepared by a hydrothermal method. The invention comprises the following specific steps: At first, that cotton cloth is carbonize at high temperature to obtain carbon cloth, weighing a proportion of nickel chloride hexahydrate and cobalt chloride hexahydrate, and mixed with hexamethylenetetramine, Dissolved in appropriate amount of deionized water, carbon cloth or active treated carbon cloth is completely immersed in the mixed solution, stirred for a certain time, then Ni-Co double hydroxide is grown on the carbon cloth under hydrothermal conditions, and thecarbon cloth after reaction is washed and dried to obtain Ni-Co double hydroxide supercapacitor electrode material with carbon cloth as a flexible substrate.