Abstract: In order to reduce sensitivity of binocular pupil detection system to the pupil position, a binocular pupil detector based on near-infrared telecentric lens is designed. Calculation process of optical parameters of near-infrared telecentric lens is described. Telecentric lens is designed and optimized in different parts with Zemax.Tolerance is analyzed by MTF, maximum distortion of the whole field and object telecentricity. Finally, standard circle is used to calibrate the instrument to find out fitting correspondence between number of pixels and pupil size. Results show that pupil diameter measurement accuracy reaches 0.05 mm for interpupillary distance of 55 mm to 75 mm, which can meet the requirements.