The invention provides a carbon cloth surface modification method used for a flexible supercapacitor electrode. The carbon cloth surface modification method comprises the following steps that S1: firstly the carbon cloth is arranged in the mixed solution of potassium permanganate and concentrated acid to perform first step of reaction, then the deionized water is added to perform second step of reaction, finally hydrogen peroxide is added and the carbon oxide cloth is prepared, then the carbon oxide cloth is repeatedly washed by the deionized water and ethyl alcohol in turn to the neutral state and dried; and S2: finally the carbon oxide cloth after drying processing of the step S1 is calcinated and reduced by sodium amide under the nitrogen environment and then repeatedly washed by the deionized water and the ethyl alcohol in turn until the washing solution is neutral and dried so as to obtain the surface modified carbon cloth. The modified carbon cloth prepared by the method is uniform in surface and high in specific capacitance, and the capacitance retention rate is more than 85% when the current density is increased to 20mA/cm2 from 1mA/cm2 so as to have excellent rate performance. Besides, the method is simple in technology, low in cost and simple in industrial promotion.