The invention belongs to the field of valves, and particularly relates to a pneumatic cast steel gate valve. The pneumatic cast steel gate valve is characterized in that a through hole is formed in the bottom of a valve body; the diameter of the upper portion of the through hole is smaller than that of the lower portion; a wedge disc is located in a valve cavity and clamped between a first fixing seat and a second fixing seat; the bottom of the wedge disc is connected with a sealing cover through a connecting rod; the lower end of the connecting rod is arranged in the through hole; the diameter of the connecting rod is smaller than that of the through hole; the sealing cover is as big as the through hole, and the lower end of the sealing cover is arranged outside the through hole; a liquid receiving box is fixed to the bottom of the valve body and communicates with the through hole; one end of a connecting pipe communicates with the liquid receiving box, and the other end of the connecting pipe communicates with a fluid outlet; a micro pump and a flow meter are fixed to the connecting pipe; an air cylinder is fixed to the top of a valve deck; and one end of a valve rod is connected with the air cylinder, and the other end of the valve rod penetrates through the valve deck and the valve body to be connected with the wedge disc.