A preparation method of a high temperature alloy turbine disk billet of an aeroengine is characterized by presetting high temperature alloy powder which has similar components and is suitable for cladding on a designed high temperature alloy mandrel by a high power (above (above 5000W) CO2 laser with stable cladding property and cladding, building up by welding and forming the powder to the dimension required by a turbine disk billet, and adding at least three elements from alloy elements Ni, B, Si, Y2O3 and Hf to the preset high temperature alloy powder. The preparation method improves the existing laser cladding forming technology, and realizes a breakthrough of preparing a large homogeneous billet of the turbine disk which is a core component of the aeroengine without cracks and pore defect by the laser cladding forming technology.