Hemingway, who has done a lot to shape twentieth-century American literature, remains an interesting writer because it is possible to read him in many ways. With the rise of American nature writing, the natural world in Hemingway’s fiction has recently caught critical attention. This paper is going to explore the origin of his nature complex and ecological awareness from three aspects, that is, his life experience in nature, his reading experience and the influence of the painter Cezanne.