As the spokesman of the Jazz Age, F.Scott.Fitzgerald revealed the disillusionment of the American Dream in his master-piece TheGreatGatsbyunder the background of the 1920s, or the Jazz Age.In the novel, the protagonist Jay Gatsby devoted his life to chasing his dream but was confronted with complete corruption in the end.This paper tries to enclose the tragic roots and causes of the doom of Gatsby's dream from three dimensions, i.e. Gatsby's innocent attitude toward social class distinction, his blind faith toward ideal love, and the cruelties of society.