An action recognition system is illustrated. The action recognition system has an annular body, at least one light emitting unit, at least one light sensing unit and an action recognition module. The annular body is worn on a movable part of a user. One end of the light emitting unit is exposed on an inner side of the annular body, wherein the light emitting unit emits a first light beam illuminating at least a portion of the movable part. One end of the light sensing unit is exposed on the inner side of the annular body. The light sensing unit operatively senses a second light beam reflected by the at least portion of the movable part and generates a light sensing signal. The action recognition module is configured to operatively determine an action of the user according to the light sensing signal.