The metaphor of "teacher as stranger" is proposed by Maxine Greene, the contemporary American educational philosopher, in her 1973 work Teacher as Stranger: Contemporary Philosophy for the Modern Age. Greene claims teachers must continually struggle to clarify their self-consciousness by doing philosophy. She also hopes that teachers would take a stranger's view to notice details and patterns in their life-world instead of taking the cultural pattern for granted. Furthermore, she believes that teachers should promote students' consciousness, and free students to have self-awareness, self-selection, self-realization through the educational process. By using theoretical analysis, the paper first discusses the background of the metaphor. Secondly, it discusses the meaning of the metaphor from Greene's viewpoint. Finally, this paper proposes some implications for instruction of teachers. The implications are as follows: (1) teachers should reexamine their roles and life situations; (2) teachers should regard students as individuals'; (3) teachers should develop their pedagogy theorizing by doing philosophy; (4) teachers should be like a homecomers and notice their teaching as if they never noticed it before; (5) teachers can enlighten students' life visions by the arts; (6) teachers should select the value criteria of teaching by doing philosophy; (7) teachers should promote teachers' and students' self-consciousness.