A general detection device was designed based on the traditional scanning pentaprism and image processing methodwhich can quickly and accurately detect the parallelism of the light from collimator with aperture less than 1 meter. The influence of pentaprism attitude on device’s angle measurement accuracy was analyzed in detailand the beam parallelism of 1-meter level collimator with 30-meter focal length in the laboratorythen the focal plane according was adjusted to the measurement results. The final collimator defocus is controlled within 4 mmand the angle measurement accuracy of the device can reach within 1 ".