The utility model discloses a cutter for processing cone holes, which consists of a clamping handle and a conical cutter head which are entirely connected. One end of the cutter is a clamping handle, while the other end is the cutter head on which is arranged by a knifepoint. The utility model is characterized in that the end surface and the side surface of the knifepoint are inclined planes whose inclination degrees are 1-1.5 degrees; a main cutting edge arranged on the knifepoint is an inclined plane whose inclination angle r is equal to 0.5 degree. When the cutter of the utility model is adopted for processing, the lathy straight holes can be communicated with conical holes, and the center of the conical hole and that of the straight hole can be guaranteed to be in superposition. The roughness of the surface of the conical hole is good and the processing precision is high. The utility model has the advantages of simple operation and high production efficiency.