Aiming at a t-type electro-optical measuring turntable, several commonly used optical axis parallelism testing methods are compared, and an auxiliary equipment for optical axis detection with high precision and portability is designed to complete the optical axis parallelism between a camera and laser. The principle of the optical axis detector is introduced, the factors affecting the uncertainty of the detection is analyzed. And the all-reflecting kassegreen optical structure design is adopted to reduce the volume weight while removing the effect of wavelength on the accuracy of the detector. The optical axis detector has simple structure and high accuracy, and meets the requirements of field use.