The incident angle of a parallel light beam is hard to measure accurately under the requirement of both high precision and large measurement range. A solution based on the optical vernier principle is presented, and a corresponding measuring device is given. Compared with the former method, the suggested apparatus realizes high accuracy in a larger measurement range. The experiments on the designed apparatus show a high precision of better than 0.02u in a measurement range of ±64° and the experimental results are in accordance with analytical results in theory. The invented apparatus can be widely used in many technical areas such as aerospace, precision measurement and automatic control.