Objectives There has been growing interest in the relationship between mental illness and premorbid trauma recently. The purpose of this study was to examine the difference in symptoms, functions, and their outcomes according to the degree of trauma in patients with early psychosis. Methods The study involved 226 people who participated in the Korean Early Psychosis Cohort Study, and we divided the participants into two groups according to the degree of trauma. Positive and Negative Syndrome Scale (PANSS) and Social and Occupational Functioning Assessment Scale (SOFAS) were compared at the start of the study and at 12 months after the treatment using paired t-test and repeated measures analysis of variance. Results At the beginning of the study, there was no significant difference between the two groups. But after 12 months of treatment, the high trauma group showed less improvement in PANSS negative score, general psychopathological score, total score, and SOFAS than the low trauma group. Conclusion In patients with early psychosis and at least moderate severity of premorbid trauma, negative symptoms, general psychopathological, and social and occupational functional improvements after treatment are less.