Theodore Dreiser is famous for his work's truth and dependability, and in the novel-Sister Carrie, Dreiser draws a vivid picture of American life in the late 19th century, the vividness depends on his own experience and the influence of the Naturalism, and which help form his own philosophies on life. This paper will show Dreiser's own Naturalism by giving a detailed analysis of Hurstwood's fall. In Dreiser's eyes, the desire for Carrie is not the unique reason for Hurstwood's decline. Dreiser believes that man cannot control his own life and man is just a victim of society. In the world that society force control everything, man cannot escape from himself, from his personality. Once Hurstwood leaves Chicago for New York, his tragic ending is destined. When we explore the cause of Hurstwood's fall, we also know Dreiser's philosophy that man's fate is unpredictable in the capitalist society and the certain circumstances and social system control a man's fate, nobody can predict what the future will bring to him.