The invention discloses a special powder coating additive for pulverous expendable pattern casting, and the powder additive comprises the following components: suspending agent (15-25 wt%), rheological agent (20-25 wt%), adhesive (35-55 wt%), organosilicon defoamer (4-10 wt%) and preservative agent in balancing amount. When the special additive is prepared, various pulverous materials are weighed by the required proportion, interposed into the powder stirrer in sequence to stir for 20 to 40 minutes at a low speed and then discharged and packed. When the powder coating is prepared by adopting the additive, the powder coating additive is weighed and prepared in the ratio of refractory material and additive of 100 to (6-10). After the low-speed stirred vessel is turned on, the powder coating weighed is interposed into the stirrer in batches, the stirring time is 10 to 20 minutes, and then the powder coating is discharged and packed. The additive is utilized after the powder coating manufactured is prepared into the slurry in a certain water-to-powder ratio; therefore, the special coating has the advantages of good suspension property, high intensity, uniform coating, good thixotropy, good leveling property, glabrous surface, no bubbles, no cracks and the like. Moreover, the user can adopts the dip-coating method, the hang-coating method and the brush-coating method, the viscosity change of coating materials can be decided upon the demands of the user, and different viscosities can realize different coating thicknesses.