BACKGROUND: The immense comorbidity among disorders could be ascribed to common trans-diagnostic processes. The term trans-diagnostic has been of interest in both pathology and psychology. Trans-diagnostic treatments were created as opposed to treatments based on single-diagnosis treatments. It addresses the common underlying mechanisms in a range of comorbid disorders. Trans-diagnostic treatment is one of the new psychological treatments, and its efficacy has been proven on many psychological variables. The main focus of the current study is on designing unified trans-diagnostic interventions and their efficacy on the shared mechanisms of comorbid obsessive personality disorder with anxiety, depression, and obsessive-compulsive disorder. MATERIALS AND METHODS: the sequential transformative strategy has two stages; qualitative and quantitative. In The first and qualitative section of the research, explanatory research will be carried out to investigate the trans-diagnostic intervention using a systematic review. To validate the trans-diagnostic intervention, and simultaneously with the trans-diagnostic intervention, a questionnaire has been prepared and given to 10 psychology experts and professionals in the treatment field concerning content validity by evaluators. CONCLUSION: Designing unified trans-diagnosis interventions and their efficacy on the common mechanisms of comorbid obsessive personality disorder with anxiety, depression, and obsessive-compulsive disorder is an effective treatment method for helping those suffering from a personality disorder. Clinical psychologists, psychology experts, psychiatrists, and mental health experts are all the immediate beneficiaries of this study. Moreover, clients could benefit from this intervention with less money and time.