In the three-dimensional(3D) display based on lenticular lens,large binocular parallax is one of the major factors of visual fatigue caused by viewing stereoscopic images.As the degree of visual fatigue increases with the pupil diameter,a pupil diameter measuring device is set up to record the viewer′s pupil diameter which can be used to evaluate visual fatigue objectively when the viewers view stereoscopic images.Through the combination of subjective evaluation and objective evaluation,the visual fatigue degrees in different ranges of binocular parallax are measured.The experimental results show that the observers do not have obvious visual fatigue when the range of binocular parallax is from-0.2° to 0.2°.This range can be considered as a critical range of visual comfort.