Abstract: To meet the requirement of optical axis parallel testing for multi-band and multi-axis observation instrument, the design of portable high-precision optical axis parallel detector was proposed. In order to decrease the volume of the system, Cassegrain system was used as the collimating optical system,and the optical and structural parameters were designed and optimized by using optical design software Zemax. ZnS was used as the reticule glass substrate. Multiband coaxial optical collaboration Target was designed and the photosensitive surface of the CCD was applied to collect the laser spot. The portability and measurement accuracy were improved. The consistency error of the testing instrument was within 15. The experimental results show that the design meets the needs of the optical axis parallel measurement for the observation instrument with high precision and high speed in the outfield.