A method for preparing oryzanol from oryzanol-containing soapstock serving as a raw material, comprising the following steps: 1) alkali-alcohol thermal dissolution: adding ethanol into the raw material, heating to 50-60°C, adjusting the system to alkalescence, and dissolving the raw material to obtain a solution; 2) heat-preserved fine filtration: maintaining the temperature in the step 1), and using a precision filter to filter the solution; 3) heat-preserved ultrafiltration membrane separation: under a condition of 50-60°C, carrying out membrane separation on the filtrate by a high temperature resistant ultrafiltration membrane, and collecting membrane separation liquid in a molecular weight range of 1000-5000; 4) heat-preserved decolourisation: adding an inorganic decolouriser into the membrane separation liquid, and fully stirring and filtering the liquid to obtain decolourised liquid; 5) acid neutralisation and filtration: neutralising the decolourised liquid with dilute acid, cooling the liquid, standing the liquid to completely separate out precipitates, carrying out centrifugation, and collecting the centrifugated precipitates; 6) washing: adding ethyl acetate, ethanol at a concentration greater than 85% and purified water with a temperature of 40-45°C in sequence into the centrifugated precipitates for washing, wherein the washing is to add a washing liquid of the above solvent or solution into the centrifugated precipitates, stir and mix the product thoroughly, and centrifugate the mixture to obtain centrifugated precipitates for next step of washing; and 7) drying: drying the precipitates to obtain a finished oryzanol product, wherein in the step 1) to the step 4) the system is maintained at a temperature of 50-60°C; and wherein in the step 4), the decolouriser comprises activated clay and activated carbon at a mass ratio of 1-2:1-2, and the adding amount of the decolouriser is 3-6% by weight of the oryzanol-containing soapstock raw material. 1) alkali-alcohol thermal dissolution: adding ethanol into the raw material, heating to 50-60°C, adjusting the system to alkalescence, and dissolving the raw material to obtain a solution; 2) heat-preserved fine filtration: maintaining the temperature in the step 1), and using a precision filter to filter the solution; 3) heat-preserved ultrafiltration membrane separation: under a condition of 50-60°C, carrying out membrane separation on the filtrate by a high temperature resistant ultrafiltration membrane, and collecting membrane separation liquid in a molecular weight range of 1000-5000; 4) heat-preserved decolourisation: adding an inorganic decolouriser into the membrane separation liquid, and fully stirring and filtering the liquid to obtain decolourised liquid; 5) acid neutralisation and filtration: neutralising the decolourised liquid with dilute acid, cooling the liquid, standing the liquid to completely separate out precipitates, carrying out centrifugation, and collecting the centrifugated precipitates; 6) washing: adding ethyl acetate, ethanol at a concentration greater than 85% and purified water with a temperature of 40-45°C in sequence into the centrifugated precipitates for washing, wherein the washing is to add a washing liquid of the above solvent or solution into the centrifugated precipitates, stir and mix the product thoroughly, and centrifugate the mixture to obtain centrifugated precipitates for next step of washing; and 7) drying: drying the precipitates to obtain a finished oryzanol product,