Vasconselos, a colonial expedition romance published by the American Southern writer William Gilmore Simms in 1853, is a book with postcolonial orientations. By probing into the ambiguous binary opposition of good and evil and the characterization in the book and applying the reinterpretation of ethics and morality by Nietzsche, the conflicts of the stances between the protagonist Philip and the antagonist De Soto, represented as the dialogue of values between the colonized and colonizer, can be interpreted as a cultural code of the mechanism of the power manipulation between the subject and the other. In the light of Fredric Jameson’s “political unconscious”, this binary opposition between and evil is also represented as the contradiction of ideologemes, or value systems in a concrete historical context and in the form of moral dilemma with ambiguities. Thus, it becomes a code for the author to conceal his postcolonial impulses and a powerful instrument to polemicize implicitly for the American Indians.