The invention discloses a method for processing the outer conical surface of a shaft workpiece. The method comprises a step of corresponding adjusting the processing taper of processing equipment according to the taper of a first conical surface, a step of performing trial processing on a workpiece blank piece by using the processing equipment to form an adjustment workpiece with a conical section, a step of coloring an outer circular surface on an outer round surface of the conical section to judge whether the taper of the outer conical surface of the adjustment workpiece is equal to the taper of a first conical surface or not, and adjusting the processing taper again until the taper of the outer conical surface of the processed adjustment workpiece is equal to the taper of the first conical surface if not, and a step of formally processing the workpiece blank piece by using the adjusted processing equipment to form a processed workpiece, detecting whether a detection distance betweena large end of an outer circular surface of the processed workpiece and a reference surface on the processed workpiece is in a set distance range or not, continuing to process the outer circular surface of the processed workpiece until the detection distance is in the set distance range if the detection distance is larger than a set distance, and processing the processed workpiece to form a formed workpiece.