Based on the role-play theory, this study explores the dialectical unified relationship between the roles of teachers and students in the blended teaching model. The difference analysis is carried out from the three stages of role-play process—role determination, role performance and role construction; the unity is explained from the aspects of role standard, teaching content and teaching situation. The study shows that in blended teaching there are role positioning differences, which are based on "the relationship between teachers and students", the role performance differences that focus on "the teaching content", and the role construction differences that "take role interaction as the key". It is pointed out that the roles of teachers and students are normative ones; the interaction of the roles of teachers and students serves the teaching content; and the roles of teachers and students are unified in the teaching situation.