The main purpose of this article is to explore the prerequisite of action research. 3 postulates are drawn as follows after analyzing the connotation of action research: 1. The objects of research are action researchers' own thought and practice. 2. The purpose of research is to disclose and solve the problematic of their own thought and practice for improvement. 3. The requisite means of research is reflection. If one research meets the three postulates, it can be named as an action research. The three postulates could be used to judge whether one research belongs to action research or not? Researchers who are interested in action research can also make use of them to lead their own action researches.