The invention relates to the technical field of building auxiliary equipment. The invention further discloses a stair pouring device for a prefabricated building. The device comprises a movable base,a motor frame is fixedly installed at the top of the movable base, a motor is fixedly installed at the top of an inner cavity of the motor frame, the output end of the motor is fixedly connected withthe top end of a lead screw in a sleeved way, the bottom end of the lead screw penetrates through and extends into a rotary drum, and a gear and a limiting block are fixedly connected with the end, close to the motor, of the lead screw in a sleeving way. The invention discloses the stair pouring device for a prefabricated building. Through the combined action of the gear and a gear ring and combined effect of a supporting rod, a rotating groove and a limiting circular ring, when the gear rotates, the gear ring can drive a rotary drum to rotate together, the fluidity of concrete in the rotary drum is accelerated, layering or caking of the concrete in the rotary drum is avoided, meanwhile, under the action of balls, the friction force between the rotary drum and the limiting circular ring isreduced, the rotary drum rotates more smoothly, and caking of the concrete is prevented.