The invention discloses a water-soluble powdery metal antirust agent composition. The water-soluble powdery metal antirust agent composition comprises molybdate, p-tert-butylbenzoic acid ammonium salt, phosphite ester, arylsulfinylamino acid salt, benzotriazole formate and an inorganic alkaline agent. Through combination of the phosphite ester corrosion inhibitor, the organic salt-type corrosion inhibitor and a small amount of the alkaline inorganic salt, the water-soluble powdery metal antirust agent composition is prepared. In use, the water-soluble powdery metal antirust agent composition is dissolved in water. The water-soluble powdery metal antirust agent composition can be processed simply, is convenient for storage and transport and has excellent effects of metal corrosion inhibition and protection.