Precise low-pressure lost wax casting system

The invention discloses a precise low-pressure lost wax casting system, which comprises a heat holding furnace positioned in a low-pressure casting machine. A riser tube is inserted in the heat holding furnace. The top of the riser tube extends out of the heat holding furnace and is positioned in a center hole of a working table of the low-pressure casting machine. A hoisting steel plate is fixed on the working table of the low-pressure casting machine. A modeling steel plate is fixed on the hoisting steel plate. A sand box is fixed on the modeling steel plate. A pressing steel plate covers the top end of the sand box. A pressing device is pressed on the pressing steel plate. A combined shell is arranged in the center of the inner cavity of the sand box, is coaxial to the riser tube, and comprises a thin-wall product shell, an inner gate shell, a cross gate shell and a sprue cup shell, which are sequentially arranged from top to bottom in a penetrating manner. The lower end opening of the sprue cup shell is f