In order to reduce the alignment deviation of the imaging keratometer along the optical axis and improve the measurement accuracy of corneal diopter, a high precision imaging keratometer optical system was designed. The optical system includes imaging system and low coherence interferometry system. The imaging system consists of imaging objective, cornea, and measurement target ring, wherein the imaging objective lens adopts a double telocentric optical path design. The low-coherence interferometry system uses the grating scale to measure the displacement of the scanning mirror, and then locates the vertices of the cornea and the measuring target ring by low-coherence interference signals, achieving accurate measurement between the apex of the cornea and the distance of the measuring target ring. The imaging objective has a modulation transfer function greater than 0.4 at a maximum spatial frequency of 70 lp/mm, the distortion is less than 0.05%. The simulation results show that the system has a compact structure, good imaging quality and simple operation. It meets the demand for high precision measurement of corneal refractive power by an imaging keratometer.