High quality ultra-precise machining of aspheric surface includes machining, test, and compensation machining. In order to remove repeating installation error and decrease on-machine time of the aspheric surface, a contact on-machine measurement method is proposed in combination with a laser interferometer. Shape error of the ground surface is measured directly on the machine. The on-machine measuring principle and aspheric measuring process are studied. The measurement errors caused by positional deviation and inclination angle error are corrected in ultra-precise contact on-machine measurement process. A small aspheric surface after grinding is measured by the on-machine contact measurement method and the off-line measurement system, and the measuring results are compared to confirm the validity of the proposed method.