The invention relates to the field of industrial water treatment and in particular relates to a method for treating polymer flooding oil-extraction wastewater by employing organic modified sepiolite. The method comprises the following steps: 1) acid activation, namely adding a sepiolite raw material into a hydrochloric acid solution, mixing, stirring, filtering, washing, and drying to obtain sepiolite powder subjected to acid activation; 2) thermal activation, namely roasting and dehydrating the sepiolite powder subjected to acid activation, and cooling and grinding to obtain sepiolite powder subjected to thermal activation; 3) organic modification, namely adding the sepiolite powder subjected to thermal activation into an ethanol aqueous solution of cetyl trimethyl ammonium bromide, mixing, stirring, filtering, washing, drying and grinding to prepare the organic modified sepiolite powder; and 4) adsorption, namely regulating the pH value of the polymer flooding oil-extraction wastewater by using an acid, adding a water-soluble aluminum salt, adding the organic modified sepiolite powder obtained in the step 3) for adsorption, stirring or shaking, standing and settling. The sepiolite serves as a raw material and is low-price and readily available, the process for activation and modification of the sepiolite is simple, and the sepiolite is non-toxic and harmless, has an obvious adsorption effect, rapid in treatment and high in adsorption amount.