Over the past few years, pupillometry is proliferation in psychological studies and eye tracking measurement. Pupil size or diameter can reflect mental activities, and affect other’s feeling and decision making. In addition, the sizes of our pupils are also influenced by the top-down processing, such as perception and attention, emotion and motivation, mental effort, social cognition and so on. Studies in pupillometry also found that large pupils give others good impressions (e.g. more attractive, more positive), and· cause more positive behaviors during the interaction (e.g. trust behaviors; honest behaviors). In this paper, we reviewed the relations between pupils and our mind with the pupil’s neural mechanisms and the adaptive-gain theory based on previous publications. As an effective eye-tracking parameter, pupil could be measured by eye tracking to explore the inner cognitive processing of our human being. In this paper, controlling interference of unrelated variables (e.g., luminance, gaze position), pupillometry raw data mining (e.g., baseline correction, blink processing), and the selection of pupil indices (e.g., pupil diameter, peak value, oscillations frequency) are also discussed for the future research.