Doris Lessing, one of the most popular writers of British literature in the second half of the twentieth century, is famous for her changeable styles of works and different perspectives all over the world. Reviewing from Doris Lessing's works, Marginal Man is the main clue in her literary creation. Most of characters she created in her works are living in the cracks of changeable era and cultural transformation. From the race of blacks and whites to the free female under the colonial background in 1950s and 60s; and then from the spiritual alienation under culture shock in 1970s and 80s to the difficult living conditions of the middle-aged and the aged in her later works, all of these characters are the unique microcosm of the Marginal Man created by means of blending Lessing's own experiences and emotional imagery. All of these novels transmit the rise and fall of deep culture and the sense of vicissitudes of life. This thesis elaborates Mary, a Marginal Man in Doris Lessing's "The Grass is Singing" from three points of view--Mary's drifting, Mary's Constraints and Fears, Mary's Fleeing and Awakening. From it, we can understand that fleeing as her surviving way is to get rid of the shackles of life, moreover she bares the double loss coming from the external world and the innermost, and then she eventually makes for resistance and comes to her spiritual salvation in order to seek for her spiritual home. This thesis makes a good reflection on the real living conditions of marginal groups and guides people to establish correct social values to realize the social problems caused by marginal people and make some measures to solve some of them.