The invention relates to a method for preparing oleate soap for after treatment of wood spinning and wool-polyester blended fabric. The method prepares the oleate soap through heating reactions by using oleic acid, polyoxyethylene nonyl phenyl ether, cocoanut oil diethan olamide, trimeric sodium phosphate, sodium dodecyl sulfate, calcined soda, solid sodium hydroxide and water as raw materials. The method comprises the following steps: filling water into a reaction vessel which is provided with a thermometer and mechanical raking; putting the solid sodium hydroxide into the reaction vessel; heating the vessel to a temperature over 80 DEG C by stirring; putting the oleic acid into the vessel to keep the temperature for 10 to 20 minutes; putting the polyoxyethylene nonyl phenyl ether into the vessel; heating the vessel to a temperature of between 90 and 110 DEG C, and reserving the temperature for 25 to 35 minutes; putting the calcined soda into the vessel; putting the cocoanut oil diethan olamide, the trimeric sodium phosphate and the sodium dodecyl sulfate into the vessel after the temperature is kept for 1 hour; and cooling the vessel to a temperature below 40 DEG C by stirring to produce a finished product of the oleate soap. The oleate soap prepared by the method has strong hardwater resistance, and the fabric washed by the soap has smooth and plump hand feel.