Introduction: Trichotillomania is partly a secret and unknown disorder. Recovering from TTM is not simple. The purpose of this study was to investigate the effect of metacognitive-cognitive-behavioral intervention on severity of the symptoms of hair pulling disorder.Methods: Patients were selected on the basis of DSM-IV-TR and DSM-5 diagnostic criteria for hair pulling disorder and the instruments (MGH-HPS) were administered on them. According to single case method they received 12 sessions of 45-60 minutes per week of metacognitive -cognitive-behavioral individual intervention. A Chart was also drawn using the data of this study at the second stage.Results: The results of chart drawing showed that metacognitive-cognitive-behavioral intervention significantly reduced the symptoms of the hair pulling disorder. The results of this study supported a metacognitive-cognitive-behavioral model for hair pulling disorder.Conclusion: The model presented in this study illustrates a multidimensional approach focusing on the metacognitive-cognitive-behavioral dimensions. The intervention presented in this study is a new explanatory model. The model may promotes future research into hair pulling disorder and facilitate clinical treatment and case formulation.