It is believed that Michel Foucault‟s Madness and Civilization explores the history of madness and the relationship between reason and unreason. In his book, the unreason or madness can‟t be defined clearly. He thinks people have different cognitions and attitudes to madness in different periods of civilization. The relationship between reason and unreason changes over time. They are not opposed at the beginning instead they impact each other in life and work. In English novels, there are many descriptions of madwomen. Jean Rhys‟ Wide Sargasso Sea is the prelude of Charlotte Bronte‟s Jean Eyre. “The mad woman in the attic” in Jane Eyre is Antoinette in Wide Sargasso Sea. There are many reasons for the madness of Antoinette. What caused her madness can be interpreted well with Foucault‟s madness theory. This paper tries to prove that Antoinette‟s madness is the tragedy of racialism and colonialism and give suggestions to the construction of unreason in the human civilization.