This study presents a new (to the best of our knowledge) error separation method with a single displacement probe, named as single probe shear scanning (SPSS) method, for the on-machine optical profile measurement to overcome the problems of the existing multiprobe method like the large deviation of probe spacing and the probes' performance difference. The confocal sensor with superior dynamic range, high lateral resolution, and large measurement angle to surface is applied in this study to fulfill the measurement of the optical aspheric surface. The single probe measurement system, in which the probe fixed on a flexure hinge is driven straight within a millimeter-level travel range, is established to realize the function of the multiprobe. For the established system, a new exact profile reconstruction algorithm is built to eliminate the influences of straightness errors of the scanning stage and the systemic errors of shear stage, and to reduce the effect of the sensor drift. The reconstruction algorithms by difference measurement with two shears are studied to build the bidirectional segment stitching reconstruction method, which reduces the error accumulation and improves the reconstruction accuracy under the condition of measuring errors. A profile reconstruction method with three shears measurement is proposed to make a further improvement on the reconstruction accuracy. The proposed reconstruction method with three shears measurement is successfully employed for the on-machine measurement of an aspheric surface profile, and the evaluation results agree well with those from the Taylor profiler.