What is the contributing factors of therapeutic change, common factors or specific ingredients? This is a big problem for psychotherapists after they have solved the problem ‘whether psychotherapy is effective or not’. The paper discusses the problem from the perspective of common factor theory. The paper firstly elaborated the definition and historical development of common factor theory, then it summarized common factor theory’s current advances and its limitations. It discusses the brief history of common factor theory from two clues. First, Common factor theory becomes more and more systematic and thorough. From Saul Rosenzweig’s concept of ‘common factor’ to Carl Rogers, Jerome Frank, and Michael Lambert’s classifications, then to David Orlinsky’s generic model, Bruce Wampold’s contextual model and Lundh’s two theoretical models, the concept of common factor extends, its structure becomes clearer, and its theoretical explanatory power has greatly improved. Second, common factor theory becomes more and more evidence-based. From Saul Rosenzweig and Jerome Frank’s theoretical research, to Lester Luborsky and John Norcross’ meta-analysis, then to Michael Lambert and Bruce Wampold’s empirical research about some specific common factors (such as the alliance between therapist and client, the therapists’ ability, skill, attitudes, and personal characteristics, patient’s hope and expectancy, etc.), empirical research about common factors has become an indispensable part of contemporary psychotherapy research. However, there are still several limitations with the common factor theory. The first problem is that common factors are mostly descriptive factors coming from psychotherapy efficacy research, which only describes the ‘reasons’ but not the ‘causes’ of the problem ‘why psychotherapy is effective’. So we need to ‘reverse’ the way of thinking, and do more primary research to explain the ‘mechanism’ of therapeutic change. The second problem of the common factors theory is that it lacks enough empirical evidences to support the theory. What’s more, too much focus on common factors will result to conflict with the competent implementation of a particular treatment. The provision of independent common factors disconnected from the provision of actual treatment has deleterious consequences. Finally, although many common factors have been identified in the literature, they are not the only active ingredients of therapy. In fact, there is no conclusion on the number of common factors up until today. The common versus specific factors paradigm adopted in psychotherapy research has been considered a problematic solution to the study of complex therapeutic relationships and comparisons among different forms of treatments. Increasingly, psychotherapy theory and research of late has focused on how the common factors and the specific ingredients work together to produce the benefits of therapy. We believe both camps, which are not mutually exclusive, provide useful heuristics for testing the mechanisms of change in psychotherapy, and both are needed for the patients. Whether one is in the common factors camp or the specific ingredients camp, the goal of all mental health providers is to maximize the benefit that patients get from their treatment. To this end, a scientifically vigorous examination of the contribution of common factor theory above and beyond specific mechanisms of change is warranted.