The purpose of the study was to obtain results that can inform policy and present practical implications and alternatives for social welfare that include consideration of complex childhood trauma, emotion dysregulation, and quality of life for patients at mental health institutions. Based on empirical research methods, standardized measurement tools were used, and data were collected via a questionnaire through convenience sampling from inpatients and outpatients receiving treatment at a mental health institution in ○○, Gyeonggi, South Korea. A total of 150 questionnaires were analyzed. The results of this study are as follows. First, a negative causal relationship between complex childhood trauma and lower quality of life was revealed. Second, a positive causal relationship between complex trauma in childhood and higher emotion dysregulation was observed. Third, emotion dysregulation fully mediated the effect of complex childhood trauma on quality of life. From these results, this study established social welfare intervention plans at the policy and practice levels that can be applied to the relationships between complex childhood trauma, emotion dysregulation, and quality of life among patients at mental health institutions.