An eye detecting device includes an optical assembly, an image sensor and an arithmetic unit. The optical assembly provides a plurality of incident lights. The incident lights enter into eyes to form a plurality of glints. At least part of glints is near a pupil of the eye. The image sensor is used to capture an eye image. The eye image includes images of the glints. The arithmetic unit analyzes the gray scale value of eye image and obtains the distributions of the glints through the gray scale value. The arithmetic unit determines the position of the pupil of eye according to the distributions of the glints.