The invention discloses a vacuum casting method for a cast TiAl intermetallic compound ingot. The vacuum casting method comprises a mould, wherein a water-cooling copper disc is arranged at the bottom of the mould; a circulating cooling water channel is arranged in the water-cooling copper disc to enable a molten liquid to form a longitudinal temperature gradient extending from bottom to top; water spray cooling nozzles are arranged on one side of the first edge as well as of the second edge of the mould; a resistance heating element is arranged at the corner joint of the third edge and the fourth edge of the mould to enable the molten liquid to form a transverse temperature gradient extending from one side to the other side; the longitudinal temperature gradient and the transverse temperature gradient form a slant temperature gradient to push a solid-liquid interface from the bottom of the joint of the first edge and the second edge to the top of the joint of the third edge and the fourth edge; and a finally solidified part is located near the joint of the third edge and the fourth edge, and shrinkage cavity and porosity are concentrated at the part.