Abstract: A high-precision, good-portability testing instrument was designed, which could detect optical axis- parallelism of multi-axial system according to practical needs. The instrument was able to test the nonparallelism of system-s optical axis among visible, infrared and different laser spectrum bands. Compared with similar instruments, the instrument was characterized by utilizing total reflection structure design and did not use infrared optical glass.Meanwhile, through optimization design, the instrument avoided some disadvantageous factors that influenced precision,such as the influence of plane mirror-s wedge angle . Main structure of the instrument used completely symmetric structure design and cordwood assembly way to ensure that the test precision superiored to 5, after temperature cycle test and vibration test. The instrument meets customer requirements.