In order to address the issue of obtaining the revolving contour of surface boss and combining the revolving contours of surface bosses with that of revolution body of the casing as well as the issue of low efficiency in generation of aero-engine case milling blank model and nonuniformity of machining allowance of the milling blank model, an automatic milling blank model generation method for casing based on contour searching is proposed. In the method, discretion is used to obtain the revolving contour of a complex-shaped surface boss. The revolving contours of the bosses are rotated to a sketch plane where they are combined with the revolving contour of the revolved body. The blank contour is searched on the sketch plane considering milling and turning machining process information. Blank model with uniform machining allowance and good manufacturability is then obtained by revolving the blank contour. The method is effective and universal in milling blank generation of aero-engine casings with various bosses on the surface. Milling efficiency is improved using the blank model generated by the method due to optimized machining allowance and minimized residual cutting volume.