A novel precision casting technique for TiAl based alloy was described in this work, called the permanent mold suction casting technology，and the blades of Ti-47Al-2Si、Ti-47Al-2W-0.5Si、Ti-47Al-2W-0.5Si -0.5B were get by this technology. The structures of these blades were studied. The results of this study indicate that microstructure is sensitive to heat treatment and composition. The average grain size is 30 um before heat treatment. The grain size of TiAl based alloy is grossed by heat treatment at 1573 for 5h and furnace cooling, especially Ti-47Al-2Si. The addition of boron, the grain size of Ti-47Al-2W-0.5Si-0.5B is smaller than Ti-47Al-2W-0.5Si. The γ-TiAl based alloys have equiaxed grain in cross section, but the surface microstructure of γ-TiAl based alloys have more fine equiaxed grain than inside due to high cooling rate of mold.