In this paper, the necessary instrument and control system called the “Large Size Four-axis Measurement System” which used for measuring large size aspheric surface have been designed and established. Then the development of semi-meridian measurement method on basis of large size four-axis detection system has been reported. The measurement paths were planed and the measurement program was performed on the IPC. The method can significantly reduced the align error caused by the aspheric center which is not coincidence with the rotation platform center. With the measurement system, an aspheric surface was successfully measured; whose radius of semi-meridian was 55 mm. The experimental results show that the developed methods are simple and rapid. The measurement accuracy can satisfy requirement of aspheric surface.