1. A method for recording reading behaviour, comprising: displaying an electronic document on a display unit, wherein the electronic document comprises a plurality of parts; capturing an image sequence of a user through an image capturing unit; executing an eye-tracking procedure on the image sequence to track a movement trajectory of an eye of the user; detecting whether a sight of the eye leaves a gazing part when it is detected that the eye gazes the gazing part of the parts; calculating a reading time of the gazing part when it is detected that the sight of the eye leaves the gazing part; calculating the reading time of the gazing part when it is detected that the eye keeps gazing the electronic document and reading of the gazing part is finished; and recording the reading time to a storage space corresponding to the gazing part.