A gait analysis system includes a foot sensing unit, a knee sensing unit and a portable device. The foot sensing unit senses pressure information. The knee sensing unit senses first and second three-dimensional rotational attributes of knee. The portable device generates direction of ground reaction force according to the pressure information, the first and the second three-dimensional rotational attributes of knee and a model of direction of ground reaction force, generates knee moment according to the pressure information, the first and the second three-dimensional rotational attribute of knee, the direction of ground reaction force, length of tibia and model of knee moment, determines gait information according to a gait model and one of the pressure information, the first and the second three-dimensional rotational attributes of knee, and generates gait analysis result according to the gait information, the knee moment and the gait model.
