This paper deals with St. Thomas Aquinas' view of natural law, according to the texts in Summa Theologica the Masterpiece, to analysis St. Thomas' theories of laws. The relationship among eternal law, divine law positive laws and natural law, is the subject of this paper. Beside this, from Christian experience of grace the significant of the interrelations of human nature & supernature is increased. For St. Thomas, the law of grace & freedom is the real end or goal of natural law.Modern Catholic scholars such as John Wu, Archbishop Lou Koung, Hans Kung, J. Maritain etc., in their theories about natural law, all compared St Thomas' theory of natural law, Through their analysis we can further see the unique and outstanding thoughts of St. Thomas.