A method for kneading a dental plaster powder, characterized by comprising putting the dental plaster powder, said dental plaster powder containing hemihydrate gypsum and 0.05-0.8 part by mass inclusive, per 100 parts by mass of the hemihydrate gypsum, a polycarboxylate-type water reducing agent, and water into a bottle, air tightly sealing the bottle, and then shaking the bottle.