This paper will discuss how the structure and theme develop and compare between the Beowulf and Sir Gawain and the Green Knight. Sir Gawain and the Green Knight is generally considered as the finest of the English romances. The striking feature of this poem is its tight and organized structure, whereas most of the romances are loose in structure. This poem is composed of four fits containing traditional elements of romance: the Beheading Game; the Temptation and Hunting; the Exchange of Winnings; Returning. This process is linked together systematically, and as it goes on, certain external elements of romance come into view. There are heroic ideal, Christian humiliation and chastity, so the two themes or motifs are combined to produce a work of impressive organic unity.